1.
Western United States
–
The Western United States, commonly referred to as the American West, the Far West, or simply the West, traditionally refers to the region comprising the westernmost states of the United States. Because European settlement in the U. S. expanded westward after its founding, prior to about 1800, the crest of the Appalachian Mountains was seen as the western frontier. Since then, the frontier moved westward and eventually lands west of the Mississippi River came to be referred to as the West. The West contains several major biomes, the Western U. S. is the largest region of the country, covering more than half the land area of the United States. Given this expansive and diverse geography it is no wonder the region is difficult to specifically define, a majority of the historian respondents placed the eastern boundary of the West east of the Census definition out on the eastern edge of the Great Plains or on the Mississippi River. The survey respondents as a whole showed just how little agreement there was on the boundaries of the West, within a region as large and diverse as the Western United States, smaller areas with more closely shared demographics and geography have developed as subregions. Meanwhile, the states of Idaho, Montana, Oregon and Washington can be considered part of the Northwest or Pacific Northwest, West Texas in the Chihuahuan Desert may be considered as part of the Western U. S. Fort Worth has long laid claim to be Where the West Begins, the West is still one of the most sparsely settled areas in the United States with 49.5 inhabitants per square mile. Only Texas with 78.0 inhabitants/sq mi, Washington with 86.0 inhabitants/sq mi. and California with 213.4 inhabitants/sq mi. exceed the national average of 77.98 inhabitants/sq mi. The entire Western region has also strongly influenced by European, Hispanic or Latino, Asian and Native Americans. African and European Americans, however, continue to wield a stronger political influence because of the rates of citizenship and voting among Asians. The West also contains much of the Native American population in the U. S. particularly in the reservations in the Mountain. The Western United States has a sex ratio than any other region in the United States. Because the tide of development had not yet reached most of the West when conservation became an issue, agencies of the federal government own. National parks are reserved for activities such as fishing, camping, hiking, and boating, but other government lands also allow commercial activities like ranching, logging. The largest city in the region is Los Angeles, located on the West Coast, Other West Coast cities include San Diego, San Bernardino, San Jose, San Francisco, Oakland, Bakersfield, Sacramento, Seattle, Tacoma, and Portland. Prominent cities in the Mountain States include Denver, Colorado Springs, Phoenix, Tucson, Albuquerque, Las Vegas, Salt Lake City, Boise, El Paso, and Cheyenne. Along the Pacific Ocean coast lie the Coast Ranges, which and they collect a large part of the airborne moisture moving in from the ocean
2.
Physical geography
–
Physical geography is one of the two major sub-fields of geography. Geomorphology seeks to understand landform history and dynamics, and predict future changes through a combination of observation, physical experiment. Thus the field encompasses water in rivers, lakes, aquifers and to an extent glaciers, in which the field examines the process and dynamics involved in these bodies of water. Similar to most fields of physical geography it has sub-fields that examine the bodies of water or their interaction with other spheres e. g. limnology and ecohydrology. Glaciology is the study of glaciers and ice sheets, or more commonly the cryosphere or ice, glaciology groups the latter as continental glaciers and the former as alpine glaciers. Glaciology also has a vast array of sub-fields examining the factors and processes involved in ice sheets and glaciers e. g. snow hydrology, Biogeography is the science which deals with geographic patterns of species distribution and the processes that result in these patterns. The main stimulus for the field since its founding has been that of evolution, plate tectonics, climatology examines both the nature of micro and macro climates and the natural and anthropogenic influences on them. The field is also sub-divided largely into the climates of various regions, meteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and short term forecasting. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century, meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Pedology is the study of soils in their natural environment and it is one of two main branches of soil science, the other being edaphology. Pedology mainly deals with pedogenesis, soil morphology, soil classification, palaeogeography is a cross-disciplinary study that examines the preserved material in the stratigraphic record to determine the distribution of the continents through geologic time. Almost all the evidence for the positions of the continents comes from geology in the form of fossils or paleomagnetism, the use of this data has resulted in evidence for continental drift, plate tectonics, and supercontinents. This, in turn, has supported palaeogeographic theories such as the Wilson cycle, coastal geography is the study of the dynamic interface between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It involves an understanding of coastal weathering processes, particularly wave action, sediment movement and weathering, coastal geography, although predominantly geomorphological in its research, is not just concerned with coastal landforms, but also the causes and influences of sea level change. Oceanography is the branch of geography that studies the Earths oceans. These diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean, Quaternary science is an inter-disciplinary field of study focusing on the Quaternary period, which encompasses the last 2.6 million years. The field was founded by the German geographer Carl Troll. Landscape ecology typically deals with problems in an applied and holistic context, geomatics is the field of gathering, storing, processing, and delivering geographic information, or spatially referenced information
3.
Extensional tectonics
–
Extensional tectonics is concerned with the structures formed, and the tectonic processes associated with, the stretching of the crust or lithosphere. The types of structure and the geometries formed depend on the amount of stretching involved. Stretching is generally measured using the parameter β, known as the beta factor where β = t 0 t 1 t 0 is the initial crustal thickness and it is also the equivalent of the strain parameter stretch. In areas of relatively low crustal stretching, the dominant structures are high to moderate angle normal faults, with associated half grabens and tilted fault blocks. In areas of crustal stretching, individual extensional faults may become rotated to too low a dip to remain active. Large displacements may juxtapose syntectonic sediments against metamorphic rocks of the mid to lower crust, in some cases the detachments are folded such that the metamorphic rocks are exposed within antiformal closures and these are known as metamorphic core complexes. Passive margins above a weak layer develop a set of extensional structures. Large listric regional faults are developed with rollover anticlines and related crestal collapse grabens, on some margins, such as the Niger Delta, large counter-regional faults are observed, dipping back towards the continent, forming large grabenal mini-basins with antithetic regional faults. Areas of extensional tectonics are associated with, Rifts are linear zones of localized crustal extension. They range in width from less than 100 km up to several hundred km, consisting of one or more normal faults. In individual rift segments one polarity normally dominates giving a half-graben geometry, other common geometries include metamorphic core complexes and tilted blocks. Examples of active continental rifts are the Baikal Rift Zone and the East African Rift, divergent plate boundaries are zones of active extension as the crust newly formed at the mid-ocean ridge system becomes involved in the opening process. Zones of thickened crust, such as those formed during continent-continent collision tend to spread laterally, after the collision has finished the zone of thickened crust generally undergoes gravitational collapse, often with the formation of very large extensional faults. Large-scale Devonian extension, for example, followed immediately after the end of the Caledonian orogeny particularly in East Greenland and western Norway. When a strike-slip fault is offset along strike such as to create a gap i. e. a left-stepping bend on a sinistral fault, such bends are known as releasing bends or extensional stepovers and often form pull-apart basins or rhombochasms. Back-arc basins form behind many subduction zones due to the effects of oceanic trench roll-back which leads to a zone of extension parallel to the island arc. A passive margin built out over a layer, such as an overpressured mudstone or salt. The inboard part of the prism is affected by extensional faulting
4.
Miocene
–
The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago. The Miocene was named by Sir Charles Lyell and its name comes from the Greek words μείων and καινός and means less recent because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch, the earth went from the Oligocene through the Miocene and into the Pliocene, with the climate slowly cooling towards a series of ice ages. The Miocene boundaries are not marked by a single distinct global event, the apes arose and diversified during the Miocene, becoming widespread in the Old World. By the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path, as in the Oligocene before it, grasslands continued to expand and forests to dwindle in extent. In the Miocene seas, kelp forests made their first appearance, the plants and animals of the Miocene were fairly modern. The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy, Two subdivisions each form the lower, middle, continents continued to drift toward their present positions. Mountain building took place in western North America, Europe, both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the North American Great Plains, India continued to collide with Asia, creating dramatic new mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish–Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea near the end of the Miocene. The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture, climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a period during the Miocene when the global climate rivalled that of the Oligocene. The Miocene warming began 21 million years ago and continued until 14 million years ago, by 8 million years ago, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as 7 to 8 million years ago, life during the Miocene Epoch was mostly supported by the two newly formed biomes, kelp forests and grasslands. This allows for more grazers, such as horses, rhinoceroses, ninety five percent of modern plants existed by the end of this epoch. The higher organic content and water retention of the deeper and richer grassland soils, with long term burial of carbon in sediments, produced a carbon and this, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO2
5.
Great Basin
–
The Great Basin is the largest area of contiguous endorheic watersheds in North America. The region spans several physiographic divisions, biomes/ecoregions, and deserts, the term Great Basin is applied to hydrographic, biological, floristic, physiographic, topographic, and ethnographic geographic areas. The name was coined by John C. Frémont, who, based on information gleaned from Joseph R. Walker as well as his own travels, the hydrographic definition is the most commonly used, and is the only one with a definitive border. The other definitions yield not only different geographical boundaries of Great Basin regions, the Great Basin physiographic section is a geographic division of the Basin and Range Province defined by Nevin Fenneman in 1931. The United States Geological Survey adapted Fennemans scheme in their Physiographic division of the United States, the section is somewhat larger than the hydrographic definition. The culture area covers approximately 400,000 sq mi, or just less than twice the area of the hydrographic Great Basin, the hydrographic Great Basin is a 209,162 square miles area that drains internally. All precipitation in the region evaporates, sinks underground or flows into lakes, as observed by Frémont, creeks, streams, or rivers find no outlet to either the Gulf of Mexico or the Pacific Ocean. The region is bounded by the Wasatch Mountains to the east, the Sierra Nevada and Cascade Ranges to the west, the south rim is less distinct. The Great Basin includes most of Nevada, half of Utah, substantial portions of Oregon and California and small areas of Idaho, Wyoming, the term Great Basin is slightly misleading, the region is actually made up of many small basins. The Great Salt Lake, Pyramid Lake, and the Humboldt Sink are a few of the drains in the Great Basin, the Salton Sink is another closed basin within the Great Basin. The Great Basin Divide separates the Great Basin from the watersheds draining to the Pacific Ocean, the southernmost portion of the Great Basin is the watershed area of the Laguna Salada. The Great Basins longest and largest river is the Bear River of 350 mi, Lake Tahoe, North Americas largest alpine lake, is part of the Great Basins central Lahontan subregion. The hydrographic Great Basin contains multiple deserts and ecoregions, each with its own set of flora. The ecological boundaries and divisions in the Great Basin are unclear, the Great Basin overlaps four different deserts, portions of the hot Mojave and Colorado Deserts to the south, and the cold Great Basin and Oregon High Deserts in the north. The deserts can be distinguished by their plants, the Joshua tree and creosote bush occur in the hot deserts, the cold deserts are generally higher than the hot, and have their precipitation spread throughout the year. The climate and flora of the Great Basin is strongly dependent on elevation, as the elevation increases, because of this, forests occur at higher elevations. Utah juniper/single-leaf pinyon and mountain mahogany form open pinyon-juniper woodland on the slopes of most ranges, stands of limber pine and Great Basin bristlecone pine can be found in some of the higher ranges
6.
Snake Range
–
The Snake Range is a mountain range in White Pine County, Nevada, United States. The south-central portion of the range is included within Great Basin National Park, the range reaches a maximum elevation of 13,065 feet at the summit of Wheeler Peak, the tallest independent mountain within Nevada and the second highest point within the state. The range also contains four of the five highest mountain peaks in Nevada, typical of other ranges in the Basin and Range Province, the Snake Range runs in a north-south direction, for approximately 60 miles. To the west are Spring Valley and the Schell Creek Range, and to the east across the Utah border are Snake Valley, Sacramento Pass is where U. S. Route 6-50, the Loneliest Highway in America, crosses the range. It is the means of eastbound access to this part of eastern Nevada. Great Basin National Park is located in the section of the Snake Range. Established in 1986, it protects the unique geologic and habitat features of the range and Great Basin Desert. The southern section includes the natural rock Lexington Arch. Several large groves of ancient Great Basin Bristlecone Pine trees thrive in the Great Basin montane forests of the higher elevations. The higher elevations of the Snake Range in the section are protected by the Mount Moriah Wilderness Area. The Snake Range includes two groups of peaks, the southern section rises quickly from a point near the border with Lincoln County, reaching the summit of Granite Peak just 10 miles to the north. From there northwards the range continues to rise, passing Lincoln Peak, Mt. Washington, Pyramid Peak, Baker Peak and it finally reaching its apex at Wheeler Peak. North of Wheeler Peak the range begins to drop, reaching 7,154 feet at Sacramento Pass, Sacramento Pass is where the more remote northern section of the range begins. In just 12 miles the range rises past Silver Creek Canyon, to the north of this peak is an unusual formation, a flat plateau of sub-alpine tundra called The Table, covering about 2 square miles at an elevation of 11,000 feet. A grove of ancient Great Basin Bristlecone Pines grows on this plateau near the peak, north of The Table is another unusual geologic feature. Deadman Creek and Smith Creek, draining eastward into Snake Valley, the mouth of this canyon lies below 3, 000-foot cliffs,6,000 feet below and 6 miles away from the summit of Mt. Moriah
7.
Panamint Range
–
The Panamint Range is a short rugged fault-block mountain range in the northern Mojave Desert, within Death Valley National Park in Inyo County, eastern California. The origin of the name is the Paiute word Panümünt, the range runs north-south for approximately 100 miles through Inyo County, forming the western wall of Death Valley and separating it from the Panamint Valley to the west. The range is part of the Basin and Range Province, at the end of the Great Basin. The highest peak in the range is Telescope Peak, with an elevation of 11,049 feet, dantes View east of Death Valley is another. The Panamint Mining District is on the side of the Panamint Range. Panamint City was a town in the district, formerly in the central section of the range. The historic mining community of Ballarat, also in the district, is now a ghost town, the Gold Hill Mining District was in the southwestern section of the range, at the northeast end of Butte Valley. The Wildrose Charcoal Kilns are ruins of charcoal kilns located near Wildrose Canyon in the northern range and they were built in 1877 by the Modock Consolidated Mining Company, to provide fuel for smelters near their lead and silver mines in the Argus Range
8.
White Mountains (California)
–
The White Mountains of California and Nevada are a triangular fault-block mountain range facing the Sierra Nevada across the upper Owens Valley. They extend for approximately 60 mi as an elevated plateau about 20 mi wide on the south. The ranges broad southern end is near the community of Big Pine, the narrow northern end is at Montgomery Pass, where U. S. Route 6 crosses. The range lies within the section of the Inyo National Forest. Middle slopes from 6,500 to 8,200 ft have somewhat denser stands of piñon pine and these upper and lower conifer zones are often separated by a zone of mountain mahogany brush. Various subspecies of sagebrush extend from surrounding valleys to the alpine zone. A bristlecone pine in the part of the range is the oldest known living tree in the world. Pine nuts from piñon pine stands were harvested as a staple food by Paiute Indians whose descendants still live in adjacent valleys. The White Mountains also have small remnant groves of pine, Jeffrey pine, ponderosa pine, Sierra juniper. A number of plant species are endemic to the White Mountains, fauna include two herds of bighorn sheep, mule deer, marmots and feral horses. Permanent streams have no fish, but there are naturalized populations of trout including rare Paiute cutthroat trout which is protected from angling. Birds include Clarks nutcracker and other Corvidae which eat and cache pine nuts, cattle from ranches in surrounding valleys are still grazed under permit as high as the alpine zone. Historically sheep were grazed in large numbers, introducing diseases from which the native Bighorn Sheep populations are still slowly recovering. Before European colonization of surrounding valleys in the mid 19th century, Paiute Indians occupied summer hunting camps up to about 13,100 ft, the highest point in the range is White Mountain Peak, which at 14,252 ft is the third-highest summit in California. This peak is actually an extinct volcano rising about 1,600 ft above the plateau surface, the summit is composed of Mesozoic metavolcanic rock – lava lifted and melted by rising granite. The volcano itself is long since gone, the White Mountains are the highest range completely inside the Great Basin, although the adjacent Sierra Nevada Range along the basins western edge has two higher summits. The entire range is within the Inyo National Forest, a four-wheel drive road reaches the summit from the south to service the summit laboratory of the White Mountain Research Station. The road is normally gated seven miles from the summit at an elevation of 11,680 ft, the bench includes Mt. Hogue at 12,743 ft. and further north Mt. Dubois at 13,559 ft. the high point on the plateau
9.
Sandia Mountains
–
The Sandia Mountains are a mountain range located in Bernalillo and Sandoval counties, immediately to the east of the city of Albuquerque in New Mexico in the southwestern United States. The range is largely within the Cibola National Forest, and part of the range is protected as the Sandia Mountain Wilderness and its highest point is Sandia Crest,10,678 feet. Sandía means watermelon in Spanish, and is believed to be a reference to the reddish color of the mountains at sunset. Also, when viewed from the west, the profile of the mountains is a ridge, with a thin zone of green conifers near the top. He also notes that the Sandia Pueblo Indians call the mountain Bien Mur, the range measures approximately 17 miles north-south, and the width in the east-west direction varies from 4 to 8 miles. The west side of the range is steep and rugged, with a number of rock walls. The east side has a gentler slope, the Sandias are part of a single larger geologic unit, the Sandia-Manzano Mountains. The other part consists of the Manzano Mountains which lie to the south of the Sandias. The two ranges are separated by Tijeras Canyon, which leads to an important pass, the canyon is traversed by Interstate 40. The Sandias are the highest range in the vicinity, and are well-separated from the higher Sangre de Cristo Mountains. This gives Sandia Crest a relatively high topographic prominence of 4,098 ft. Lying to the east and northeast of the Sandias are two ranges, the Ortiz Mountains and the San Pedro Mountains. The Sandia Mountains are home to the second longest tramway. Over this distance the tram cars ascend over 4,000 feet, the average speed of the tram car is 12 mph, and the length of the ride is approximately 15 minutes. The current longest tramway as of 2010 is in Armenia, the Sandia Mountains are a fault block range, on the eastern edge of the Rio Grande Rift Valley. The Sandias were uplifted in the last ten years as part of the formation of the Rio Grande Rift. They form the boundary of the Albuquerque Basin. The core of the consists of Sandia granite, approximately 1.5 billion years old. This is topped by a thin layer of sedimentary rock of Pennsylvanian age
10.
Teton Range
–
The Teton Range is a mountain range of the Rocky Mountains in North America. A north-south range, it is mostly on Wyomings eastern side of the Idaho state line and it is south of Yellowstone National Park. Most of the east slope of the range is in Grand Teton National Park, early French Voyageurs used the name les trois tétons. It is likely that the Shoshone people once called the whole range Teewinot, other peaks in the range include Mount Moran 12,605 feet, Mount Wister 11,490 feet, Buck Mountain 11,938 feet and Static Peak 11,303 feet. Between six and nine years ago, stretching and thinning of the Earths crust caused movement along the Teton fault. The west block along the line rose to form the Teton Range. The faults east block fell to form the valley called Jackson Hole, the geological processes that led to the current composition of the oldest rocks in the Teton range began about 2.5 billion years ago. At that time, sand and volcanic debris settled into an ancient ocean, additional sediment was deposited for millions of years and eventually heat and pressure metamorphosed the sediment into gneiss. Subsequently, magma was forced up through the cracks in the gneiss to form granite, other intrusive igneous rocks are noticeable as the black dikes of diabase, visible on the southwest face of Mount Moran and on the Grand Teton. Starting during the Cambrian period, deep deposits of rock were deposited in shallow seas over the metamorphic basement rocks. 2.1 million years ago the Huckleberry Ridge Tuff was deposited along the west slope of the part of the range. One reason the Teton Range is famous is because of the elevation above the eastern side. Unlike most mountain ranges, the east side of the teton range lacks foothills and this is due to the Teton Fault at the base of the range on the eastern side, and the range being too young to have eroded into soft hills. The east slope of the Teton range rises sharply, from 5,000 to 7,000 feet above the valley floor. Jackson Hole and the Tetons have been the setting for a number of films, including John Waynes movie acting debut in The Big Trail in 1930 and the western film classic, Shane in 1953. Mount Moran and the mountains were used as a backdrop for the lake/swamp setting in the original series of Land of the Lost
11.
Mount Whitney
–
Mount Whitney is the highest summit in the contiguous United States and the Sierra Nevada, with an elevation of 14,505 feet. The west slope of the mountain is in Sequoia National Park, the east slope is in the Inyo National Forest in Inyo County. The summit of Whitney is on the Sierra Crest and the Great Basin Divide and it lies near many of the highest peaks of the Sierra Nevada. The peak rises dramatically above the Owens Valley, sitting 10,778 feet or just over two miles above the town of Lone Pine 15 miles to the east, in the Owens Valley. It rises more gradually on the west side, lying only about 3,000 feet above the John Muir Trail at Guitar Lake, the mountain is partially dome-shaped, with its famously jagged ridges extending to the sides. Mount Whitney is above the line and has an alpine climate. Very few plants grow near the summit, one example is the Skypilot, the only animals are transient, such as the butterfly Parnassius phoebus and the gray-crowned rosy finch. The mountain is the highest point on the Great Basin Divide, waterways on the west side of the peak flow into Whitney Creek, which flows into the Kern River. The Kern River terminates in the Tulare Basin, during very wet years, water overflows from the Tulare Basin into the San Joaquin River which flows to the Pacific Ocean. From the east, water from Mount Whitney flows to Lone Pine Creek, which joins the Owens River, which in turn terminates at Owens Lake, the estimated elevation of the summit of Mount Whitney has changed over the years. The technology of elevation measurement has become refined and, more importantly. The peak was commonly said to be at 14,494 ft, an older plaque on the summit reads elevation 14,496.811 feet but this was estimated using the older vertical datum from 1929. Since then the shape of the Earth has been estimated more accurately, using a new vertical datum established in 1988 the benchmark is now estimated to be at 14,505 ft. The rise is caused by a fault system that runs along the eastern base of the Sierra. Thus, the granite that forms Mount Whitney is the same as the granite that forms the Alabama Hills, the raising of Whitney is due to the same geological forces that cause the Basin and Range Province, the crust of much of the intermontane west is slowly being stretched. The granite that forms Mount Whitney is part of the Sierra Nevada batholith, in Cretaceous time, masses of molten rock that originated from subduction rose underneath what is now Whitney and solidified underground to form large expanses of granite. In July 1864, the members of the California Geological Survey named the peak after Josiah Whitney, during the same expedition, geologist Clarence King attempted to climb Whitney from its west side, but stopped just short. In 1871, King returned to climb what he believed to be Whitney, upon learning of his mistake in 1873, King finally completed his own first ascent of Whitney, but did so a month too late to claim the first recorded ascent
12.
Pico de Orizaba
–
Pico de Orizaba, also known as Citlaltépetl, is a stratovolcano, the highest mountain in Mexico and the third highest in North America, after Denali of the United States and Mount Logan of Canada. It rises 5,636 metres above sea level in the end of the Trans-Mexican Volcanic Belt. The volcano is currently dormant but not extinct, with the last eruption taking place during the 19th century and it is the second most prominent volcanic peak in the world after Africas Mount Kilimanjaro. Pico de Orizaba overlooks the valley and city of Orizaba, from which it gets its name, the name Citlaltépetl is not used by Nahuatl speakers of the Orizaba area, who instead call it Istaktepetl, or White Mountain. In the earliest mention of the volcano, it was referred to by the natives during the Pre-Columbian Era as Poyautécatl, Citlaltépetl was the common name in the Náhuatl language when the Spanish arrived in Mexico. Citlaltépetl comes from the Náhuatl citlalli and tepētl and thus means Star Mountain and this name is thought to be based on the fact that the snow-covered peak can be seen year round for hundreds of kilometers throughout the region. A legend from the city of Coscomatepec tells of how the planet Venus can be seen settling into the crater of Citlaltépetl, during the colonial era, the volcano was also known as Cerro de San Andrés due to the nearby settlement of San Andrés Chalchicomula at its base. A third name, Poyauhtecatl, which means the one that colors or illuminates, has also been recorded and this name was given by the Tlaxcaltecas in memory of their lost country. The peak of Citlaltépetl rises dramatically to an elevation of 5,636 m above sea level, it has a topographic prominence of 4,922 m. Regionally dominant, Pico de Orizaba is the highest peak in Mexico, Orizaba is ranked 7th in the world in topographic prominence. It is the second most prominent volcanic peak in the world after Africas Mount Kilimanjaro, the topography of Pico de Orizaba is asymmetrical from the center of the crater, the eastern face is the steepest side of the volcano and the northwestern face the most gradual side. The gradual slopes of the face of the volcano allows for the presence of large glaciers and is the most traveled route to take for hikers traveling to the summit. Pico de Orizaba is one of three volcanoes in México that continue to support glaciers and is home to the largest glacier in Mexico. Orizaba has nine known glaciers, Gran Glaciar Norte, Lengua del Chichimeco, Jamapa, Toro, Glaciar de la Barba, Noroccidental, Occidental, Suroccidental, the equilibrium line altitude is not known for Orizaba. Snow on the south and southeast sides of the volcano melts quickly because of solar radiation, the insolation angle and wind redeposition on the northwest and north sides allow for constant accumulation of snow providing a source for the outlet glaciers. On the north side of Orizaba, the Gran Glaciar Norte fills the elongated highland basin and is the source for seven outlet glaciers. The main glacier extends 3.5 km north of the rim, has a surface area of about 9.08 km2 descending from 5,650 m to about 5,000 m. It has an irregular and stepped profile that is caused in part by the configuration of the bedrock
13.
White Mountain Peak
–
It is the fourteenth most topographically prominent peak in the contiguous United States. The effects of altitude on physiology are studied at the Barcroft Station, there is a winding dirt road leading to the summit station that is usually cleared of snow between late June and November. Access is restricted to only by a locked gate about 2 miles before Barcroft station. Open gate days are typically 2 Sundays in the summer, the normal round trip hike from the gate is about 14 miles round trip with less than 2,600 feet of vertical gain. However, there are two different dips in the trail of about 250 feet each, adding up to an elevation gain during the roundtrip of over 3500 feet. The open gate shaves about 4 miles and 790 feet of gain off the round trip and this route is popular with mountain bikers. The peak is approached from the north where it is guarded by a narrow arête or knife-edge ridge. A better nontechnical alternative to the road would be to drive as far as possible up Leidy Canyon from Fish Lake Valley. From the flats it is an easy traverse south into the cirque of the North Fork, a moderate scramble up the ridge between the North Branch and the larger cirque of the main North Fork leads to the easier upper slopes of the peak. While the peak does not require climbing skills, it still poses a serious challenge to hikers because of the high altitude. The summit and the station at 12,470 feet has an alpine tundra climate. Most of the mountain, however, has a warm summer continental climate or semi-arid climate, winters are extremely severe, with the peak receiving upwards of 13 feet of snow annually. List of mountain peaks of California List of highest points in California by county List of Ultras of the United States White Mountain Peak, special Collections & Archives, UC San Diego Library
14.
California
–
California is the most populous state in the United States and the third most extensive by area. Located on the western coast of the U. S, California is bordered by the other U. S. states of Oregon, Nevada, and Arizona and shares an international border with the Mexican state of Baja California. Los Angeles is Californias most populous city, and the second largest after New York City. The Los Angeles Area and the San Francisco Bay Area are the nations second- and fifth-most populous urban regions, California also has the nations most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The Central Valley, an agricultural area, dominates the states center. What is now California was first settled by various Native American tribes before being explored by a number of European expeditions during the 16th and 17th centuries, the Spanish Empire then claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its war for independence. The western portion of Alta California then was organized as the State of California, the California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom. If it were a country, California would be the 6th largest economy in the world, fifty-eight percent of the states economy is centered on finance, government, real estate services, technology, and professional, scientific and technical business services. Although it accounts for only 1.5 percent of the states economy, the story of Calafia is recorded in a 1510 work The Adventures of Esplandián, written as a sequel to Amadis de Gaula by Spanish adventure writer Garci Rodríguez de Montalvo. The kingdom of Queen Calafia, according to Montalvo, was said to be a land inhabited by griffins and other strange beasts. This conventional wisdom that California was an island, with maps drawn to reflect this belief, shortened forms of the states name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, various estimates of the native population range from 100,000 to 300,000. The Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups also were diverse in their organization with bands, tribes, villages. Trade, intermarriage and military alliances fostered many social and economic relationships among the diverse groups, the first European effort to explore the coast as far north as the Russian River was a Spanish sailing expedition, led by Portuguese captain Juan Rodríguez Cabrillo, in 1542. Some 37 years later English explorer Francis Drake also explored and claimed a portion of the California coast in 1579. Spanish traders made unintended visits with the Manila galleons on their trips from the Philippines beginning in 1565
15.
Badwater Basin
–
Badwater Basin is an endorheic basin in Death Valley National Park, Death Valley, Inyo County, California, noted as the lowest point in North America, with an elevation of 282 ft below sea level. Mount Whitney, the highest point in the contiguous 48 United States, is only 84.6 miles to the north west. The site itself consists of a small spring-fed pool of bad water next to the road in a sink, the pool does have animal and plant life, including pickleweed, aquatic insects, and the Badwater snail. Adjacent to the pool, where water is not always present at the surface, repeated freeze–thaw, the pool is not the lowest point of the basin, the lowest point is several miles to the west and varies in position, depending on rainfall and evaporation patterns. The salt flats are hazardous to traverse, and so the sign marking the low point is at the pool instead, the basin was considered the lowest elevation in the Western Hemisphere until the discovery of Laguna del Carbón in Argentina at −344 ft. At Badwater Basin, significant rainstorms flood the valley bottom periodically, newly formed lakes do not last long though, because the 1.9 in of average rainfall is overwhelmed by a 150 in annual evaporation rate. This is the greatest evaporation potential in the United States, meaning that a 12 ft lake could dry up in a single year, when the basin is flooded, some of the salt is dissolved, it is redeposited as clean crystals when the water evaporates. A popular site for tourists is the sign marking sea level on the cliff above the Badwater Basin, numerous evaporation cycles and a lack of outflow caused an increasing hypersalinity, typical for endorheic bodies of water. Over time, this hypersalinization, combined with sporadic rainfall and occasional aquifer intrusion, has resulted in periods of briny soup, or salty pools, on the lowest parts of Death Valleys floor. Salts began to crystallize, coating the surface with the thick crust, ranging from 3 to 60 in, Death Valley pupfish List of elevation extremes by country List of elevation extremes by region John McKinney, Californias Desert Parks, A Day Hikers Guide. Wilderness Press 2006, ISBN 0-89997-389-2, S. 54–55 Don J. Easterbrook, geological Society of America 2003, ISBN 94-592-0504-6, S. 63–64 Badwater Basin in the Encyclopædia Britannica
16.
Death Valley
–
Death Valley is a desert valley located in Eastern California. It is one of the hottest places in the world at the height of summertime along with deserts in Africa, Death Valleys Badwater Basin is the point of the lowest elevation in North America, at 282 feet below sea level. This point is 84.6 miles east-southeast of Mount Whitney, Death Valleys Furnace Creek holds the record for the highest reliably recorded air temperature in the world,134 °F on July 10,1913. This has been contested by other weather experts and it is located mostly in Inyo County, California. It has an area of about 3,000 sq mi, the highest point in Death Valley itself is Telescope Peak in the Panamint Range, which has an elevation of 11,043 feet. Death Valley is one of the best geological examples of a basin and it lies at the southern end of a geological trough known as Walker Lane, which runs north into Oregon. The valley is bisected by a right lateral slip fault system, represented by the Death Valley Fault. The eastern end of the left lateral Garlock Fault intersects the Death Valley Fault, Furnace Creek and the Amargosa River flow through the valley but eventually disappear into the sands of the valley floor. Death Valley also contains salt pans, according to current geological consensus, at various times during the middle of the Pleistocene era, inland lakes formed in Death Valley. Lake Manly received water overflowing from a chain of other Pleistocene lakes, Death Valley has a subtropical, hot desert climate, with long, extremely hot summers and short, warm or mild winters, as well as little rainfall. As a general rule, lower altitudes tend to have higher temperatures, when the sun heats the ground, that heat is then radiated upward, but the dense below-sea-level air absorbs some of this radiation and radiates some of it back towards the ground. In addition, the valley walls trap rising hot air and recycle it back down to the valley floor. This process is important in Death Valley, as it provides its specific climate. The valley is surrounded by mountains, while its surface is flat and devoid of plants, so much of the suns heat can reach the ground, absorbed by soil. When air at ground level is heated, it begins to rise, moving up past steep, high mountain ranges, which then cools slightly, sinking back down towards the valley more compressed. This air is reheated by the sun to a higher temperature, moving up the mountain again, whereby the air moves up and down in a circular motion in cycles. This heated air increases ground temperature markedly, forming the hot wind currents that are trapped by atmospheric pressure and mountains, Death Valley holds temperature records because it has an unusually high number of factors that lead to high atmospheric temperatures. The depth and shape of Death Valley influence its summer temperatures, the valley is a long, narrow basin 282 feet below sea level, yet is walled by high, steep mountain ranges
17.
Ecoregion
–
An ecoregion is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are less or greater than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, the biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. Three caveats are appropriate for all bio-geographic mapping approaches, firstly, no single bio-geographic framework is optimal for all taxa. Ecoregions reflect the best compromise for as many taxa as possible, secondly, ecoregion boundaries rarely form abrupt edges, rather, ecotones and mosaic habitats bound them. Thirdly, most ecoregions contain habitats that differ from their assigned biome, biogeographic provinces may originate due to various barriers. Some physical, some climatic and some ocean chemical related, the history of the term is somewhat vague as it was used in many contexts, forest classifications, biome classifications, biogeographic classifications, etc. The concept of ecoregion of Bailey gives more importance to ecological criteria, while the WWF concept gives more importance to biogeography, there is significant, but not absolute, spatial correlation among these characteristics, making the delineation of ecoregions an imperfect science. Such transition zones are called ecotones, Ecoregions can be categorized using an algorithmic approach or a holistic, “weight-of-evidence” approach where the importance of various factors may vary. An example of the approach is Robert Bailey’s work for the U. S. The intended purpose of ecoregion delineation may affect the method used, according to WWF, the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. WWF has identified 867 terrestrial ecoregions, and approximately 450 freshwater ecoregions across the Earth, the use of the term ecoregion is an outgrowth of a surge of interest in ecosystems and their functioning. In particular, there is awareness of issues relating to spatial scale in the study and it is widely recognized that interlinked ecosystems combine to form a whole that is greater than the sum of its parts. The Global 200 is the list of ecoregions identified by WWF as priorities for conservation, Terrestrial ecoregions are land ecoregions, as distinct from freshwater and marine ecoregions. In this context, terrestrial is used to mean of land, WWF ecologists currently divide the land surface of the Earth into 8 major ecozones containing 867 smaller terrestrial ecoregions. The WWF effort is a synthesis of previous efforts to define. Many consider this classification to be decisive, and some propose these as stable borders for bioregional democracy initiatives. The eight terrestrial ecozones follow the major floral and faunal boundaries, identified by botanists and zoologists, ecozone boundaries generally follow continental boundaries, or major barriers to plant and animal distribution, like the Himalayas and the Sahara
18.
Clarence Dutton
–
Clarence Edward Dutton was an American geologist and US Army officer. Dutton was born in Wallingford, Connecticut on May 15,1841, in 1875 he began work as a geologist for the U. S. Geological Survey. He helped coordinate the response to a large earthquake in the Mexican state of Sonora in 1887. He was elected a member of the National Academy of Sciences in 1884, in 1886, Dutton led a USGS party to Crater Lake, Oregon. His team carried a half-ton survey boat, the Cleetwood, up the mountain slope. From the Cleetwood, Dutton used piano wire with lead weights to measure the depth of the lake at 168 different points, the survey team determined the lake was 1,996 feet deep. The currently-accepted maximum depth figure, measured by sonar, is 1,943 feet, Dutton was a close associate of John Wesley Powell, G. K. Gilbert, and William Henry Holmes at the USGS and he was an energetic and effective field geologist, in 1875-1877 Duttons field party mapped 12,000 square miles of the high plateaus of southern Utah, an area of rugged topography and poor access. Dutton had a flair for literary description, and is best remembered today for his colorful descriptions of the geology. Dutton first taught the world to look at that country and see it as it was, Dutton is almost as much the genius loci of the Grand Canyon as Muir is of Yosemite -- Wallace Stegner, Beyond the Hundredth Meridian. In 1891 he retired from the USGS to serve as commander of the arsenal of San Antonio, Texas, after retiring from the Army in 1901, he returned to the study of geology. Dutton spent his last years at the home of his son in Englewood,1880, Report on the Geology of the High Plateaus of Utah. Survey of the Rocky Mountain Region, vol,1882, Tertiary History of the Grand Canyon District. Survey Monograph 2,264 pp. and atlas,1889, The Charleston Earthquake of August 31,1886. 1889, On Some of the Greater Problems of Physical Geology,1904, Earthquakes, in the light of the new seismology Biographical memoir at the National Academy of Sciences Stegner, Wallace. Beyond the Hundredth Meridian, John Wesley Powell and the Second Opening of the West and this article incorporates text from a publication now in the public domain, Gilman, D. C. Thurston, H. T. Colby, F. M. eds. article name needed, works by or about Clarence Dutton at Internet Archive
19.
North America
–
North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be considered a subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16. 5% of the land area. North America is the third largest continent by area, following Asia and Africa, and the fourth by population after Asia, Africa, and Europe. In 2013, its population was estimated at nearly 565 million people in 23 independent states, or about 7. 5% of the worlds population, North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge. The so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago, the Classic stage spans roughly the 6th to 13th centuries. The Pre-Columbian era ended with the migrations and the arrival of European settlers during the Age of Discovery. Present-day cultural and ethnic patterns reflect different kind of interactions between European colonists, indigenous peoples, African slaves and their descendants, European influences are strongest in the northern parts of the continent while indigenous and African influences are relatively stronger in the south. Because of the history of colonialism, most North Americans speak English, Spanish or French, the Americas are usually accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass previously unknown by Europeans. In 1507, Waldseemüller produced a map, in which he placed the word America on the continent of South America. He explained the rationale for the name in the accompanying book Cosmographiae Introductio, for Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespuccis name, but in its feminine form America, following the examples of Europa, Asia and Africa. Later, other mapmakers extended the name America to the continent, In 1538. Some argue that the convention is to use the surname for naming discoveries except in the case of royalty, a minutely explored belief that has been advanced is that America was named for a Spanish sailor bearing the ancient Visigothic name of Amairick. Another is that the name is rooted in a Native American language, the term North America maintains various definitions in accordance with location and context. In Canadian English, North America may be used to refer to the United States, alternatively, usage sometimes includes Greenland and Mexico, as well as offshore islands
20.
Fault scarp
–
A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other. It is the expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old geologic fault. Fault scarps often contain highly fractured rock of both hard and weak consistency, in many cases, bluffs form from the upthrown block and can be very steep. The height of the formation is equal to the vertical displacement along the fault. This movement is usually episodic, with the height of the bluffs being the result of multiple movements over time, displacement of around 5 to 10 meters per tectonic event is common. Due to the dramatic uplift along the fault, the scarp is very prone to erosion. Weathering, mass wasting and water runoff can soon wear down these bluffs, adjacent V-shaped valley formations give the remaining fault spurs a very triangular shape. This formation is known as a triangular facet, however, this landform is not limited to fault scarps, Fault scarps may be only a few centimeters or many meters high. Fault-line scarps are coincident with faults, but are most typically formed by the erosion of rocks that have been brought alongside more resistant ones by the movement along the fault. Teton Range The Teton Range in Wyoming is an example of a fault scarp. The dramatic topography of the Tetons is due to the recent activity on the Teton Fault. Hurricane Cliffs The Hurricane Cliffs, west of Zion National Park in Utah is a prominent example of a fault scarp along an old, essentially inactive, other examples include the scarps bounding the East African Rift Valley and the Rio Grande Rift in New Mexico. Sources Easterbrook, D. J. Surface processes and landforms, prentice Hall, Upper Saddle River, New Jersey
21.
Sierra Nevada (U.S.)
–
The Sierra Nevada is a mountain range in the Western United States, between the Central Valley of California and the Basin and Range Province. The vast majority of the lies in the state of California. The Sierra runs 400 miles north-to-south, and is approximately 70 miles across east-to-west, the Sierra is home to three national parks, twenty wilderness areas, and two national monuments. These areas include Yosemite, Sequoia, and Kings Canyon National Parks, the character of the range is shaped by its geology and ecology. More than one hundred years ago during the Nevadan orogeny. The range started to uplift four M. A. ago, the uplift caused a wide range of elevations and climates in the Sierra Nevada, which are reflected by the presence of five life zones. Uplift continues due to faulting caused by forces, creating spectacular fault block escarpments along the eastern edge of the southern Sierra. The Sierra Nevada has a significant history, the California Gold Rush occurred in the western foothills from 1848 through 1855. Due to inaccessibility, the range was not fully explored until 1912, the Sierra Nevada lies in Central and Eastern California, with a very small but historically important spur extending into Nevada. West-to-east, the Sierra Nevadas elevation increases gradually from 1,000 feet in the Central Valley to an height of about 10,500 feet at its crest only 50–75 miles to the east. The east slope forms the steep Sierra Escarpment, unlike its surroundings, the range receives a substantial amount of snowfall and precipitation due to orographic lift. The Sierra Nevada stretches from the Susan River and Fredonyer Pass in the north to Tehachapi Pass in the south and it is bounded on the west by Californias Central Valley and on the east by the Basin and Range Province. The geographical boundary between the Sierra and the Cascades is virtually indistinguishable, with the Fredonyer Pass designation being traditional, physiographically, the Sierra is a section of the Cascade-Sierra Mountains province, which in turn is part of the larger Pacific Mountain System physiographic division. The range is drained on its western slope by the Central Valley watershed, the northern third of the western Sierra is part of the Sacramento River watershed, and the middle third is drained by the San Joaquin River. The eastern slope watershed of the Sierra is much narrower, its rivers flow out into the endorheic Great Basin of eastern California and western Nevada. Although none of the eastern rivers reach the sea, many of the streams from Mono Lake southwards are diverted into the Los Angeles Aqueduct which provides water to Southern California, the height of the mountains in the Sierra Nevada increases gradually from north to south. Between Fredonyer Pass and Lake Tahoe, the range from 5,000 feet to more than 9,000 feet. The crest near Lake Tahoe is roughly 9,000 feet high, farther south, the highest peak in Yosemite National Park is Mount Lyell
22.
Wasatch Fault
–
Not to be confused with the Wasatch Front The Wasatch Fault is an active fault located primarily on the western edge of the Wasatch Mountains in the U. S. state of Utah. The fault is 240 miles long, stretching from southern Idaho, through northern Utah and it is made up of several segments, on average 25 miles long, each of which can independently produce earthquakes as powerful as local magnitude 7.5. The Wasatch Fault is a fault which forms the eastern boundary of the Basin. The Wasatch Mountains have been uplifted and tilted to the east by movement of the fault, the average rate of uplift along the fault over its history is approximately 1 millimetre per year, although there are indications that more rapid slip has occurred in the past few thousand years. During the past 6,000 years, an earthquake has occurred approximately once every 350 years somewhere along one of the central segments of the Wasatch Fault. The segments that underlie Salt Lake City and Provo produce an earthquake on average every 1,300 years. The last major earthquake on the Salt Lake City segment was about 1,300 years ago, the urban areas of the Wasatch Front lie on soft lake sediments, a remnant of Lake Bonneville. An earthquake on the Wasatch Fault could severely damage gas, electric, water, communication, the report predicts that when the quake strikes, it could kill up to 6,200 people, injure at least 90,000, and cause US$40 billion in economic losses. At least 42% of all buildings along the Wasatch Front could be at least moderately damaged, the earthquake danger was not known when many structures were built in the area, as many hospitals and schools are located atop the faults themselves. Massive landslides are another major threat, USGS factsheet Utah Geological Survey Public Information Series 40, The Wasatch Fault Utah Geological Survey presentation about the fault
23.
Colorado Plateau
–
The province covers an area of 337,000 km2 within western Colorado, northwestern New Mexico, southern and eastern Utah, and northern Arizona. About 90% of the area is drained by the Colorado River and its tributaries, the Green, San Juan. Most of the remainder of the plateau is drained by the Rio Grande, the Colorado Plateau is largely made up of high desert, with scattered areas of forests. In the southwest corner of the Colorado Plateau lies the Grand Canyon of the Colorado River, much of the Plateaus landscape is related, in both appearance and geologic history, to the Grand Canyon. The nickname Red Rock Country suggests the brightly colored rock left bare to the view by dryness, domes, hoodoos, fins, reefs, river narrows, natural bridges, and slot canyons are only some of the additional features typical of the Plateau. The Colorado Plateau has the greatest concentration of U. S. National Park Service units in the country outside of the Washington, DC metropolitan area. Among its ten National Parks are Grand Canyon, Glen Canyon, Zion, Bryce Canyon, Capitol Reef, Canyonlands, Arches, Mesa Verde, and Petrified Forest. The province is bounded by the Rocky Mountains in Colorado, and by the Uinta Mountains and Wasatch Mountains branches of the Rockies in northern and it is also bounded by the Rio Grande Rift, Mogollon Rim and the Basin and Range Province. Isolated ranges of the Southern Rocky Mountains such as the San Juan Mountains in Colorado, north-south trending normal faults that include the Hurricane, Sevier, Grand Wash, and Paunsaugunt separate the sections component plateaus. This fault pattern is caused by the forces pulling apart the adjacent Basin and Range province to the west. Occupying the southeast corner of the Colorado Plateau is the Datil Section, thick sequences of mid-Tertiary to late-Cenozoic-aged lava covers this section. Development of the province has in part been influenced by structural features in its oldest rocks. Part of the Wasatch Line and its various faults form the edge of the province. Faults that run parallel to the Wasatch Fault that lies along the Wasatch Range form the boundaries between the plateaus in the High Plateaus Section, the Uinta Basin, Uncompahgre Uplift, and the Paradox Basin were also created by movement along structural weaknesses in the regions oldest rock. Some sources also include the Tushar Mountain Plateau as part of the Colorado Plateau, the mostly flat-lying sedimentary rock units that make up these plateaus are found in component plateaus that are between 1500 m to over 3350 m above sea level. A supersequence of these rocks is exposed in the various cliffs, within these rocks are abundant mineral resources that include uranium, coal, petroleum, and natural gas. Study of the unusually clear geologic history has greatly advanced that science. A rain shadow from the Sierra Nevada far to the west, higher areas receive more precipitation and are covered in forests of pine, fir, and spruce
24.
Rio Grande rift
–
The Rio Grande Rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east, the rift extends from central Colorado in the north to the state of Chihuahua, Mexico in the south. The rift zone consists of four basins that have a width of 50 kilometers. The rift can be observed on location at Rio Grande National Forest, White Sands National Monument, Santa Fe National Forest, the Rio Grande Rift has been an important site for humans for a long time, because it provides a north-south route that follows a major river. The Rio Grande follows the course of the rift from southern Colorado to El Paso, important cities, including Albuquerque, Santa Fe, Taos, Española, Las Cruces, El Paso, and Ciudad Juárez lie within the rift. The Rio Grande Rift represents the easternmost manifestation of widespread extension in the western U. S. during the past 35 million years, the rift consists of three major basins and many smaller basins, less than 100 km2. The three major basins are the San Luis, Española, and Albuquerque basins, further south, the rift is defined by a network of smaller, less topographically distinct alternating basins and ranges. The distinction between these basins and those of the Basin and Range Province becomes blurred in northern Mexico. Basin size generally decreases to the north in the rift, where the Española covers approximately 120 km north-south and 40 km east-west, the Albuquerque basin is the largest of the three basins, spanning 160 km north-south and 86 km east-west at its widest points. It is the oldest of the three basins, and contains 7,350 m of Paleogene clastic sediments deposited on Precambrian basement. The southernmost Albuquerque basin contains pre-rift volcanic deposits, while the central, the southernmost Rio Grande Rift broadens, becoming more complex in structure and physiographically indistinguishable from the adjoining Basin and Range province. In cross-section, the geometry of the basins within the rift are asymmetrical half-grabens, with major fault boundaries on one side, which side of the basin has the major fault or the hinge alternates along the rift. The alternation between these half-grabens occurs along transfer faults, which trend across the rift to connect the major basin-bounding faults, flanking mountains are generally taller along the east side of the rift. The thickness of the crust increases to the north beneath the rift, the crustal thickness underneath the rift is on average 30–35 km, thinner by 10–15 km than the Colorado Plateau on the west and the Great Plains to the east. The rift is presently nearly tectonically quiescent, but significant deformation and this extension is associated with very low seismic velocities in the upper mantle above approximately 400 km depth associated with relatively hot mantle and low degrees of partial melting. This intrusion of the asthenosphere into the lithosphere and continental crust is thought to be responsible for all of the volcanism associated with the Rio Grande rift. The sedimentary fill of the basins consists largely of alluvial fan, the most alkalic lavas erupted outside the rift. The sediments that were deposited during rifting are commonly known as the Santa Fe Group and this group contains sandstones, conglomerates, and volcanics
25.
Columbia Plateau
–
The Columbia Plateau is a geologic and geographic region that lies across parts of the U. S. states of Washington, Oregon, and Idaho. It is a flood basalt plateau between the Cascade Range and the Rocky Mountains, cut through by the Columbia River. In one of various usages, the term Columbia Basin refers to more or less the area as the Columbia Plateau. Over a period of perhaps 10 to 15 million years, lava flow after lava flow poured out, as the molten rock came to the surface, the Earths crust gradually sank into the space left by the rising lava. Many of these formations are subdivided into formal and informal members, the subsidence of the crust produced the large plateau—a large, slightly depressed lava plain sometimes also known as the Columbia Basin. The ancient Columbia River was forced into its present course by the advancing lava. The lava, as it flowed over the area, first filled the stream valleys, entities found in these lake beds include fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals. Columbia River Basin Ethnic History Archive
26.
Trans-Mexican Volcanic Belt
–
The Trans-Mexican Volcanic Belt, also known as the Transvolcanic Belt and locally as the Sierra Nevada, is a volcanic belt that covers central-southern Mexico. Several of its highest peaks have snow all year long, and during clear weather, the Trans-Mexican Volcanic Belt spans across Central-Southern Mexico from the Pacific Ocean to the Gulf of Mexico between 18°30N and 21°30N, resting on the southern edge of the North American Plate. This approximately 1000 kilometer long, 90–230 km broad structure is an east-west, active, continental volcanic arc, encompassing an area of approximately 160,000 km2. Over several million years, the subduction of the Rivera and Cocos plates beneath the North American Plate along the end of the Middle America Trench formed the Trans-Mexican Volcanic Belt. In addition to the complexities, igneous compositions vary—dominant subduction related products contrast with intraplate geo-chemical signatures. These features are related to the reactivation of early fault systems during the Trans-Mexican Volcanic belts evolution. The main brittle fault systems geometry, kinematics, and age define an array of what could be multiple factors affecting the deformation of the belt. It exhibits many features, not limited to large stratovolcanoes, including monogenetic volcano cones, shield volcanoes, lava dome complexes. Prior to the formation of the Trans-Mexican Volcanic Belt, an older, but related volcanic belt, from the Late Eocene to the Middle Miocene, counterclockwise rotation of the volcanic arc transitioned the once active Sierra Madre Occidental to a now active Trans-Mexican Volcanic Belt. By the Middle Miocene, the transition from the silicic to more mafic compositions was complete, due to the orthogonal orientation of the Trans-Mexican Volcanic Belt in relation to the trend of Mexican tectonic provinces, its Pre-Cretaceous basement is highly heterogeneous. The Trans-Mexican Volcanic Belt east of 101°W rests upon Precambrian terranes, assembled into the Oaxaquia microcontinent, assemblage of these basement rocks results with a thickness of 50–55 km east of 101°W and 35–40 km west of 101°W. The subducting plates originated from the breakup of the Farallon Plate at approximately 23 Ma, the Rivera Plate was the last fragment detached from the Cocos Plate, becoming a microplate at around 10 Ma. This small plate is bounded by the Rivera fracture zone, the East Pacific Rise, the Tamayo fracture zone, and the Middle American Trench. The larger Cocos Plate is bordered by the North American Plate and the Caribbean Plate to the northeast, the Pacific Plate to the west, the Cocos and Rivera are relatively young oceanic plates that are subducting along the Middle American Trench at different convergence rates. Middle Miocene adakitic rocks are found furthest from the trench and along the front of the central Trans-Mexican Volcanic Belt during the Pliocene-Quaternary. It has been suggested that slab melting contributed to the imprint on the Trans-Mexican Volcanic Belt. The plate boundary geometry and sub-horizontal subducting slabs thermal structure are the factors for initial arc volcanism. The oldest rocks of this age may be exposed near the volcanic front
27.
Mexico
–
Mexico, officially the United Mexican States, is a federal republic in the southern half of North America. It is bordered to the north by the United States, to the south and west by the Pacific Ocean, to the southeast by Guatemala, Belize, and the Caribbean Sea, and to the east by the Gulf of Mexico. Covering almost two million square kilometers, Mexico is the sixth largest country in the Americas by total area, Mexico is a federation comprising 31 states and a federal district that is also its capital and most populous city. Other metropolises include Guadalajara, Monterrey, Puebla, Toluca, Tijuana, pre-Columbian Mexico was home to many advanced Mesoamerican civilizations, such as the Olmec, Toltec, Teotihuacan, Zapotec, Maya and Aztec before first contact with Europeans. In 1521, the Spanish Empire conquered and colonized the territory from its base in Mexico-Tenochtitlan, Three centuries later, this territory became Mexico following recognition in 1821 after the colonys Mexican War of Independence. The tumultuous post-independence period was characterized by instability and many political changes. The Mexican–American War led to the cession of the extensive northern borderlands, one-third of its territory. The Pastry War, the Franco-Mexican War, a civil war, the dictatorship was overthrown in the Mexican Revolution of 1910, which culminated with the promulgation of the 1917 Constitution and the emergence of the countrys current political system. Mexico has the fifteenth largest nominal GDP and the eleventh largest by purchasing power parity, the Mexican economy is strongly linked to those of its North American Free Trade Agreement partners, especially the United States. Mexico was the first Latin American member of the Organisation for Economic Co-operation and Development and it is classified as an upper-middle income country by the World Bank and a newly industrialized country by several analysts. By 2050, Mexico could become the fifth or seventh largest economy. The country is considered both a power and middle power, and is often identified as an emerging global power. Due to its culture and history, Mexico ranks first in the Americas. Mexico is a country, ranking fourth in the world by biodiversity. In 2015 it was the 9th most visited country in the world, Mexico is a member of the United Nations, the World Trade Organization, the G8+5, the G20, the Uniting for Consensus and the Pacific Alliance. Mēxihco is the Nahuatl term for the heartland of the Aztec Empire, namely, the Valley of Mexico, and its people, the Mexica and this became the future State of Mexico as a division of New Spain prior to independence. It is generally considered to be a toponym for the valley became the primary ethnonym for the Aztec Triple Alliance as a result. After New Spain won independence from Spain, representatives decided to name the new country after its capital and this was founded in 1524 on top of the ancient Mexica capital of Mexico-Tenochtitlan
28.
Mexican Plateau
–
The Central Mexican Plateau, also known as the Mexican Altiplano, is a large arid-to-semiarid plateau that occupies much of northern and central Mexico. A low east-west mountain range in the state of Zacatecas divides the plateau into northern and southern sections and these two sections, called the Northern Plateau and Central Plateau, are now generally regarded by geographers as sections of one plateau. The Mexican Plateau is mostly covered by deserts and xeric shrublands, with forests covering the surrounding mountain ranges. The Mexican Altiplano is one of six distinct sections of the Basin and Range Province. In phytogeography, the Sonoran Desert is within the Sonoran Floristic Province of the Madrean Region in southwestern North America, various narrow, isolated ridges cross the Mesa del Norte and numerous depressions also dot the region, the largest of which is the Bolsón de Mapimí. The Río Bravo del Norte and its tributary, the Río Conchos, drain portions of the plateau. Both drain to the Gulf of Mexico, much of the northern plateau comprises internal drainage basins that do not drain to the sea. The Mesa Central or southern plateau is higher than its northern counterpart, the southern plateau contains numerous valleys originally formed by ancient lakes. It extends across the states of Aguascalientes, Jalisco, Zacatecas, Guanajuato, Querétaro, Michoacán, México, several of Mexicos most prominent cities, including Mexico City and Guadalajara, are located in the valleys of the southern plateau. Much of the plateau is drained by the Río Grande de Santiago and its tributaries, including the Río Lerma. Tributaries of the Río Pánuco drain the eastern portion of the southern plateau, the Central Mexican matorral covers much of the southern plateau, with the subtropical Bajío dry forests occupying the lower portions of the Lerma–Río Grande de Santiago basin. Higher altitudes are covered by Mixed Forests, then Temperate Coniferous Forests and this article incorporates public domain material from the Library of Congress Country Studies website http, //lcweb2. loc. gov/frd/cs/. Ricketts, Taylor H. Eric Dinerstein, David M. Olson, Colby J. Loucks, terrestrial Ecoregions of North America, a Conservation Assessment. Image Science and Analysis Laboratory, NASA-Johnson Space Center, earth from Space - Image Information
29.
Laramide orogeny
–
The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous,70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute, the Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The phenomenon is named for the Laramie Mountains of eastern Wyoming, the Laramide orogeny is sometimes confused with the Sevier orogeny, which partially overlapped it in time and space. The orogeny is commonly attributed to events off the west coast of North America, most hypotheses propose that oceanic crust was undergoing flat-slab subduction, i. e. One cause for shallow subduction may have been a rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust, magmatism associated with subduction occurred not near the plate edges, but far to the east, called the Coast Range Arc. Geologists call such a lack of volcanic activity near a subduction zone a magmatic null and this particular null may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter asthenosphere. One result of angle of subduction and the drag that it caused was a broad belt of mountains. Part of the proto-Rocky Mountains would be modified by extension to become the Basin. According to paleontologist Thomas M. Lehman, the Laramide orogeny triggered the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction, the Laramide orogeny produced intermontane structural basins and adjacent mountain blocks by means of deformation. This style of deformation is typical of continental plates adjacent to convergent margins of long duration that have not sustained continent/continent collisions and this tectonic setting produces a pattern of compressive uplifts and basins, with most of the deformation confined to block edges. Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon, the basins contain several thousand meters of Paleozoic and Mesozoic sedimentary rocks that predate the Laramide orogeny. As much as 5,000 meters of Cretaceous and Cenozoic sediments filled these orogenically-defined basins, deformed Paleocene and Eocene deposits record continuing orogenic activity. During the Laramide orogeny, basin floors and mountain summits were much closer to sea level than today, after the seas retreated from the Rocky Mountain region, floodplains, swamps, and vast lakes developed in the basins. Drainage systems imposed at that time persist today, since the Oligocene, episodic epeirogenic uplift gradually raised the entire region, including the Great Plains, to present elevations. Topographically, the basin floors resemble the surface of the western Great Plains, at most boundaries, Paleozoic through Paleogene units dip steeply into the basins off uplifted blocks cored by Precambrian rocks. The eroded steeply dipping units form hogbacks and flatirons, many of the boundaries are thrust or reverse faults. Although other boundaries appear to be monoclinal flexures, faulting is suspected at depth, most bounding faults show evidence of at least two episodes of Laramide movement, suggesting both thrust and strike-slip types of displacement
30.
Sierra Madre Oriental
–
The Sierra Madre Oriental is a mountain range in northeastern Mexico. The northernmost are the Sierra del Burro and the Sierra del Carmen which reach the border with the United States at the Rio Grande, north of the Rio Grande, the range continues northwestward into Texas and beyond as the Davis and Guadalupe Ranges. Mexicos Gulf Coastal Plain lies to the east of the range, the Mexican Plateau, which averages 1,100 metres in elevation, lies between the Sierra Madre Oriental and the Sierra Madre Occidental further west. The climate of the Sierra Madre Oriental is drier than the rainforest areas further south. The highest point is Cerro San Rafael, at 3,700 metres above sea level, is the highest point of the Sierra Madre Oriental and the state of Coahuila and the second in Mexico in isolation. This long range of mountains is noted for its abundant biodiversity and large number of endemic species of plants and wildlife. The Sierra Madre Oriental pine-oak forests are found at elevations in the range. Much of the wildlife can also be found in the Sierra Madre Occidental, which runs parallel to these mountains along western Mexico. Pine-oak forests are dominated by species of pine, such as Pinus nelsonii, P. cembroides, P. pseudostrobus, and P. arizonica. Matorral is characterized by woody shrubs, small trees, cacti, montane chaparral is found above 1,700 m and is home to species in the genera Quercus, Arbutus, Yucca, Cercocarpus and Bauhinia. Piedmont scrub occurs below 2,000 m and is composed of plants 3 to 5 m in height such as Helietta parvifolia, birds of the forest include the Mexican chickadee, Montezuma quail, Stricklands woodpecker, zone-tailed hawk and several species of jay. Pine-oak forests in Coahuila are part of the route of monarch butterflies. Original habitats have been reduced by clearance for livestock grazing and logging over hundreds of years. Protected areas include the Cumbres de Monterrey National Park in Mexico, the El Cielo Biosphere in Tamaulipas preserves the northernmost tropical Veracruz moist forests in Mexico and extensive temperate cloud forests. Mountain peaks of Mexico Sierra Madre Oriental pine-oak forests
31.
Gulf of California
–
The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland. It is bordered by the states of Baja California, Baja California Sur, Sonora, rivers which flow into the Gulf of California include the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and the Yaqui. The gulfs surface area is about 160,000 km2, the Gulf is thought to be one of the most diverse seas on the planet, and is home to more than 5,000 species of micro-invertebrates. Home to over a people, Baja California is one of the longest peninsulas in the world. Parts of the Gulf of California are a UNESCO World Heritage Site, the International Hydrographic Organization defines the southern limit of the Gulf of California as, A line joining Piastla Point in Mexico, and the southern extreme of Lower California. The Gulf of California is 1,126 km long and 48–241 km wide, with an area of 177,000 km2, a depth of 818.08 m. Transition zones exist between regions, and they usually vary for each individual species. The temperature of the water in the Gulf of California generally experiences lows of 16 °C in winter, but temperatures can vary greatly in the gulf, and the water is almost always warmer by the coast than the open ocean. For example, the waters surrounding La Paz reach 30 °C in August, while the waters in neighboring city Cabo San Lucas, occasionally, the northern Gulf of California will go through significantly cold winters. The water in the Northern Gulf can sometimes drop below 8 °C, the animals most susceptible to the large decrease in water temperature include macroscopic algae and plankton. As part of process, the East Pacific Rise propagated up the middle of the Gulf along the seabed. This extension of the East Pacific Rise is often referred to as the Gulf of California Rift Zone, the Gulf would extend as far as Indio, California, except for the tremendous delta created by the Colorado River. This delta blocks the sea from flooding the Mexicali and Imperial Valleys, volcanism dominates the East Pacific Rise. The island of Isla Tortuga is one example of ongoing volcanic activity. Furthermore, hydrothermal vents due to extension tectonic regime, related to the opening of the Gulf of California, are found in the Bahía de Concepción, the narrow sea is home to a unique and rich ecosystem. The unusual resident populations of fin whales and sperm whales do not migrate annually, the area near the delta of the Colorado river has a small remnant population of the totoaba fish. This region has historically been a magnet for world-class sport fishing activities, the region also has a rich history as a commercial fishery. However, the data vary wildly according to the species being studied, moreover, changes in terrestrial ecology, such as the vast reduction in flow from the Colorado River into the Gulf, have negatively affected fisheries, particularly in the northern region
32.
Baja California Peninsula
–
The Baja California Peninsula is a peninsula in Northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California, the peninsula extends 1,247 km from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south. It ranges from 40 km at its narrowest to 320 km at its widest point and has approximately 3,000 km of coastline, the total area of the Baja California Peninsula is 143,390 km2. The peninsula is separated from mainland Mexico by the Gulf of California, there are four main desert areas on the peninsula, the San Felipe Desert, the Central Coast Desert, the Vizcaíno Desert and the Magdalena Plain Desert. The land of California existed as a myth among European explorers before it was discovered, the earliest known mention of the idea of California was in the 1510 romance novel Las Sergas de Esplandián by Spanish author Garci Rodríguez de Montalvo. Its first expedition reached the Gulf of California and California, nevertheless, the idea of the island persisted for well over a century and was included in many maps. 1532, Hernán Cortés sends three ships North along the coast of Mexico in search of the Island of California, the three ships disappear without a trace. 1533, Cortés sends a mission to search for the lost ships. Pilot Fortún Ximénez leads a mutiny and founds a settlement in the Bay of La Paz before being killed,1539, Francisco de Ulloa explores both coasts. 1690s–1800s, Spanish settlement and colonization in lower Las Californias, the first Spanish missions in Baja California are established by Jesuit missionaries,1701, The first report and a map showing California as a peninsula rather than an island is sent to Europe. 1767, Jesuits expelled, Franciscans take over the Baja missions,1769, Franciscans go with the Portola expedition to establish new missions in Alta California. Control of the existing Baja missions passes to the Dominican Order,1773, Francisco Palóus line demarcates Franciscan and Dominican areas of mission control. 1804, Las Californias divided into Alta and Baja California, using Palóus line, 1810–1821, Mexican War of Independence 1821, First Mexican Empire, Baja California Territory established, covering Baja California Peninsula. 1847, The Battle of La Paz and the Siege of La Paz occurs,1848, Treaty of Guadalupe Hidalgo cedes Alta California to the United States. As a U. S. territory it receives the California Gold Rush,1850, California admitted to U. S. statehood. 1853, William Walker, with 45 men, captures the city of La Paz. Mexico forces him to retreat a few months later, 1930–31, The Territory of Baja California is further divided into Northern and Southern territories. 1952, The North Territory of Baja California becomes the 29th State of Mexico, the southern portion, below 28°N, remains a federally administered territory
33.
Sierra Madre Occidental
–
The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through Northwestern and Western Mexico, and along the Gulf of California. The Spanish name sierra madre means mother mountains and occidental means western in English, the range extends from northern Sonora state near the Mexico-U. S. Border at Arizona, southeastwards to the Trans-Mexican Volcanic Belt and Sierra Madre del Sur ranges, the high plateau that is formed by the range is cut by deep river valleys. This plateau is formed from volcanic rock overlying a basement of metamorphic rock and this uplift has caused changes in weather patterns, increased rainfall occurring in the mountains has provided areas where ecosystems can form in wetter areas than surrounding land. This water-source forms watersheds that provide the arid surroundings with water makes it possible to irrigate. The wet ecosystems are islands of biodiversity, differing significantly from what would otherwise be a desert landscape, oak forests are the predominant plant life and extend into the low land deserts. The major industries in the area now are agriculture and forestry, which have become contentious because of land degradation, the range trends from the north to southeast. Canyons cut by the rivers of the wet western slopes exist in addition to those of the northeast slopes, the mountains range from 300 km from the Gulf of California in the north, but begin to approach within 50 km of the Pacific in the south. These mountains are considered to be part of the much larger American cordillera. The Sierra Tarahumara or Tarahumara range is the name for the region of the Sierra Madre beginning at the Durango border and this name comes from the Tarahumara natives. This is a landscape of steep mountains formed by a high plateau that has been cut through with canyons including Copper Canyon, larger and, in places. This plateau has an elevation of 2,250 m with most of the more eroded canyons on the western slope. The highest elevations occur in the Tarahumara range, the exact elevations of the highest peaks are not known within accurate enough ranges to determine the relative elevation of peaks. The highest point is probably Cerro Mohinora, located at 25°57′N 107°03′W, estimates for the height of the mountain start around 3,040 m and go up to 3,300 m. However, Cerro Barajas, at 26°24′N 106°5′W, may be as high as 3,300 m although other sources give 3,170 m as the elevation, Cerro Gordo, at 23°12′N 104°57′W, may have an elevation between 3,350 m and 3,340 m. The southern end of the mountains may be referred to as the Sierra Huichola, in this area the Sierra Madre begin to give way to the basin and range province. Subranges of this include the Sierra de Alica and the Sierra Pajaritos both in Nayarit. The mountains act as a source of water, in an arid environment from the increased precipitation from the mountain range
34.
Endorheic basin
–
Such a basin may also be referred to as a closed or terminal basin or as an internal drainage system. However, in a basin, rain that falls within it does not flow out but may only leave the drainage system by evaporation. The bottom of such a basin is occupied by a salt lake or salt pan. Endorheic regions, in contrast to regions which flow to the ocean in geologically defined patterns, are closed hydrologic systems. Their surface waters drain to inland terminal locations where the water evaporates or seeps into the ground, endorheic water bodies include some of the largest lakes in the world, such as the Aral Sea and the Caspian Sea, the worlds largest saline inland sea. Most endorheic basins are arid, although there are notable exceptions, such as the Valley of Mexico, the Lake Tahoe region. Endorheic basins can be massively and rapidly affected by change and excessive water removal. An exorheic lake naturally remains at a level, so water flow into the lake may be many times more than is needed to maintain its present size. In contrast, an endorheic basin does not have enough inflow that it overflows to the ocean, endorheic lakes are bodies of water that do not flow into the sea. Most of the water falling on Earth finds its way to the oceans through a network of rivers, lakes, however, there is a class of water bodies that are located in closed or endorheic watersheds where the topography prevents their drainage to the oceans. These endorheic watersheds are often called terminal lakes or sink lakes, endorheic lakes are usually in the interior of a landmass, far from an ocean in areas of relatively low rainfall. Their watersheds are often confined by natural geologic land formations such as a mountain range, the inland water flows into dry watersheds where the water evaporates, leaving a high concentration of minerals and other inflow erosion products. Over time this input of erosion products can cause the lake to become relatively saline. Endorheic regions can occur in any climate but are most commonly found in desert locations, the Black Sea was likely such a lake, having once been an independent hydrological system before the Mediterranean Sea broke through the terrain separating the two. Lake Bonneville was another such lake, overflowing its basin in the Bonneville flood, malheur/Harney Lake in Oregon is normally cut off from drainage to the ocean, but has an outflow channel to the Malheur River that is normally dry, but flows in years of peak precipitation. Examples of relatively humid regions in endorheic basins often exist at high elevation and these regions tend to be marshy and are subject to substantial flooding in wet years. The area containing Mexico City is one case, with annual precipitation of 850 mm. Endorheic regions tend to be far inland with their boundaries defined by mountains or other features that block their access to oceans
35.
Las Vegas
–
The city anchors the Las Vegas Valley metropolitan area and is the largest city within the greater Mojave Desert. Las Vegas is an internationally renowned major resort city known primarily for its gambling, shopping, fine dining, entertainment and it is the leading financial, commercial, and cultural center for Nevada. The city bills itself as The Entertainment Capital of the World and it is a top three destination in the United States for business conventions and a global leader in the hospitality industry, claiming more AAA Five Diamond hotels than any city in the world. Today, Las Vegas annually ranks as one of the worlds most visited tourist destinations. The citys tolerance for numerous forms of adult entertainment earned it the title of Sin City, and has made Las Vegas a popular setting for literature, films, television programs, Las Vegas was settled in 1905 and officially incorporated in 1911. At the close of the 20th century, it was the most populated American city founded within that century, population growth has accelerated since the 1960s, and between 1990 and 2000 the population nearly doubled, increasing by 85. 2%. Rapid growth has continued into the 21st century, and according to a 2013 estimate, perhaps the earliest visitors to the Las Vegas area were nomadic Paleo-Indians, who traveled there 10,000 years ago, leaving behind petroglyphs. Anasazi and Paiute tribes followed at least 2,000 years ago, a young Mexican scout named Rafael Rivera is credited as the first non-Native American to encounter the valley, in 1829. Trader Antonio Armijo led a 60-man party along the Spanish Trail to Los Angeles, the area was named Las Vegas, which is Spanish for the meadows, as it featured abundant wild grasses, as well as desert spring waters for westward travelers. The year 1844 marked the arrival of John C, frémont, whose writings helped lure pioneers to the area. Downtown Las Vegas Fremont Street is named after him, eleven years later members of the LDS Church chose Las Vegas as the site to build a fort halfway between Salt Lake City and Los Angeles, where they would travel to gather supplies. The fort was abandoned several years afterward, the remainder of this Old Mormon Fort can still be seen at the intersection of Las Vegas Boulevard and Washington Avenue. Las Vegas was founded as a city in 1905, when 110 acres of adjacent to the Union Pacific Railroad tracks were auctioned in what would become the downtown area. In 1911, Las Vegas was incorporated as a city,1931 was a pivotal year for Las Vegas. At that time, Nevada legalized casino gambling and reduced residency requirements for divorce to six weeks and this year also witnessed the beginning of construction on nearby Hoover Dam. The influx of workers and their families helped Las Vegas avoid economic calamity during the Great Depression. The construction work was completed in 1935, in 1941, the Las Vegas Army Air Corps Gunnery School was established. Currently known as Nellis Air Force Base, it is home to the team called the Thunderbirds
36.
Lithosphere
–
A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural satellite that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a planet, the crust, is defined on the basis of its chemistry. Earths lithosphere includes the crust and the uppermost mantle, which constitute the hard, the lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, the study of past and current formations of landscapes is called geomorphology. The concept of the lithosphere as Earth’s strong outer layer was described by A. E. H, love in his 1911 monograph Some problems of Geodynamics and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term lithosphere. The concept was based on the presence of significant gravity anomalies over continental crust and these ideas were expanded by Reginald Aldworth Daly in 1940 with his seminal work Strength and Structure of the Earth and have been broadly accepted by geologists and geophysicists. The temperature at which olivine begins to deform viscously is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle, the mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick, the thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. H ∼2 κ t Here, h is the thickness of the mantle lithosphere, κ is the thermal diffusivity for silicate rocks. The age is equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years and this is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite, lamproite, and other volcanic pipes. The histories of these xenoliths have been investigated by many methods, such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics. Cryosphere Geosphere Kola Superdeep Borehole Plate tectonics Solid Earth Chernicoff, Stanley, Whitney, earths Crust, Lithosphere and Asthenosphere Crust and Lithosphere
37.
Crust (geology)
–
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
38.
Mantle (geology)
–
The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
39.
Fault (geology)
–
In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock-mass movement. Large faults within the Earths crust result from the action of tectonic forces. Energy release associated with movement on active faults is the cause of most earthquakes. A fault plane is the plane that represents the surface of a fault. A fault trace or fault line is the intersection of a plane with the ground surface. A fault trace is also the line commonly plotted on maps to represent a fault. Since faults do not usually consist of a single, clean fracture, the two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the wall occurs above the fault plane. This terminology comes from mining, when working a tabular ore body, because of friction and the rigidity of rocks, they cannot glide or flow past each other easily, and occasionally all movement stops. A fault in ductile rocks can also release instantaneously when the rate is too great. The energy released by instantaneous strain-release causes earthquakes, a common phenomenon along transform boundaries, slip is defined as the relative movement of geological features present on either side of a fault plane, and is a displacement vector. A faults sense of slip is defined as the motion of the rock on each side of the fault with respect to the other side. In practice, it is only possible to find the slip direction of faults. Based on direction of slip, faults can be categorized as, strike-slip. Dip-slip, offset is predominantly vertical and/or perpendicular to the fault trace, oblique-slip, combining significant strike and dip slip. The fault surface is usually vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are known as sinistral faults. Those with right-lateral motion are known as dextral faults
40.
Horst (geology)
–
In physical geography and geology, a horst is the raised fault block bounded by normal faults or graben. A horst is a block of the Earths crust that has lifted, or has remained stationary. Horst is Dutch and German for heap, the Vosges Mountains in France and Black Forest in Germany are examples of horsts, as are the Table, Jura and the Dole mountains. In many rift basins around the world, the vast majority of discovered hydrocarbons are found in conventional traps associated with horsts. Basin and range topography Fault-block mountain Plateau This article incorporates text from a now in the public domain, Chisholm, Hugh
41.
Graben
–
In geology, a graben is a depressed block of the Earths crust bordered by parallel faults. Graben is German for ditch or trench, the plural form is either graben or grabens. A graben is a valley with an escarpment on each side caused by the displacement of a block of land downward. Graben often occur side-by-side with horsts, horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the wall is downward. The faults typically dip toward the center of the graben from both sides, horsts are parallel blocks that remain between graben, the bounding faults of a horst typically dip away from the center line of the horst. Single or multiple graben can produce a rift valley, in many rifts, the graben are asymmetric, with a major fault along only one of the boundaries, and these are known as half-graben. The polarity of the bounding faults typically alternates along the length of the rift. The asymmetry of a half-graben strongly affects syntectonic deposition, comparatively little sediment enters the half-graben across the main bounding fault because of footwall uplift on the drainage systems. The exception is at any offset in the bounding fault. Most of the sediment will enter the half-graben down the hanging wall side. S. Central Graben, North Sea Viking Graben, North Sea Fossa
42.
Continental crust
–
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its composition is more felsic compared to the oceanic crust. The continental crust consists of layers, with a bulk composition that is intermediate to felsic. The average density of continental crust is about 2.7 g/cm3, less dense than the material that makes up the mantle. Continental crust is less dense than oceanic crust, whose density is about 2.9 g/cm3. At 25 to 70 km, continental crust is thicker than oceanic crust. About 40% of Earths surface is occupied by continental crust. It makes up about 70% of the volume of Earths crust, because the surface of continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life. There is little evidence of continental crust prior to 3.5 Ga, all continental crust ultimately derives from the fractional differentiation of oceanic crust over many eons. This process has been and continues today primarily as a result of the associated with subduction. In contrast to the persistence of continental crust, the size, shape, different tracts rift apart, collide and recoalesce as part of a grand supercontinent cycle. There are currently about 7 billion cubic kilometers of continental crust, the relative permanence of continental crust contrasts with the short life of oceanic crust. Because continental crust is less dense oceanic crust, when active margins of the two meet in subduction zones, the oceanic crust is typically subducted back into the mantle. Continental crust is rarely subducted.01 Ga, whereas the oldest oceanic crust is from the Jurassic, Continental crust and the rock layers that lie on and within it are thus the best archive of Earths history. The height of mountain ranges is usually related to the thickness of crust and this results from the isostasy associated with orogeny. The crust is thickened by the compressive forces related to subduction or continental collision, the buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, the thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. The edges of continental fragments formed this way are termed passive margins, igneous rock may also be underplated to the underside of the crust, i. e. adding to the crust by forming a layer immediately beneath it
43.
Subduction
–
Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Plates include both oceanic crust and continental crust, stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that have a rate of volcanism, earthquakes. Subduction zones are sites of convective downwelling of Earths lithosphere, subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate. The descending slab, the plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of approximately twenty-five to forty-five degrees to Earths surface and this sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere is, on average, denser. At a depth of approximately 80–120 kilometers, the basalt of the oceanic crust is converted to a rock called eclogite. At that point, the density of the oceanic crust increases and provides additional negative buoyancy and it is at subduction zones that Earths lithosphere, oceanic crust, sedimentary layers and some trapped water are recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, subduction is the driving force behind plate tectonics, and without it, plate tectonics could not occur. Subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins, subduction zones burrow deeply but are imperfectly camouflaged, and geophysics and geochemistry can be used to study them. Not surprisingly, the shallowest portions of subduction zones are known best, subduction zones are strongly asymmetric for the first several hundred kilometers of their descent. They start to go down at oceanic trenches and their descents are marked by inclined zones of earthquakes that dip away from the trench beneath the volcanoes and extend down to the 660-kilometer discontinuity. Subduction zones are defined by the array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths than elsewhere on Earth, such deep earthquakes may be driven by deep phase transformations, thermal runaway, the subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the slab bends downward
44.
Farallon Plate
–
The Farallon Plate was an ancient oceanic plate that began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic period. It is named for the Farallon Islands, which are located just west of San Francisco, over time, the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate. These fragments from elsewhere are called terranes, much of western North America is composed of these accreted terranes. The understanding of the Farallon Plate is rapidly evolving as details from seismic tomography provide improved details of the submerged remnants, since the North American west coast shows a convoluted structure, significant work has been required to resolve the complexity. In 2013 a new and more nuanced explanation emerged, proposing two additional now-subducted plates which would account for some of the complexity. As data accumulated, a view developed that one large oceanic plate, the Farallon plate, acted as a conveyor belt, conveying terranes to North Americas west coast. As the continent overran the subducting Farallon plate, the plate became subducted into the mantle below the continent. When the plates converged, the oceanic plate sank into the mantle to form a slab below the lighter continent. However this simple model was unable to explain many terrane complexities, one such large slab wall runs from north-west Canada to the eastern U. S. and extends to Central America, this slab wall had traditionally been associated with the subducting Farallon plate. Sigloch and Mihalynuk proposed that the Farallon should be partitioned into Northern Farallon, Angayucham, Mezcalera, the overridden segment is replaced by an incipient South Farallon trench. 160–155 Myr ago the Rocky Mountain deformation begins, recorded by a synorogenic clastic wedge, the Franciscan subduction complex on the South Farallon plate begins. 125 Myr ago the collision of the North America margin with an archipelago of terranes begins and this broad expanse causes strong deformations and creates the Sevier Mountains and the Canadian Rocky Mountains. 124–90 Myr ago the Omenica magmatic belts are formed in the Pacific Northwest along with a gradual override of the Mezcalera promontory by the Pacific Northwest,85 Myr ago the South Farallon trench moves westward after accretion of the Shatsky Rise Conjugate plateau. Sonora volcanism results from the slab sinking, the Tarahumara ignimbrite province is formed. 85–55 Myr ago Strong transpressive coupling of Farallon plate to terranes produces the buoyant Shatsky Rise, the Laramide orogeny results from basement uplift more than 1,000 km inland. 72–69 Myr ago the Angayucham arc, is overridden by North America, northward shuffle of Insular terrane, Intermontane terrane, and Angayucham terranes along margin. 55–50 Myr ago saw the override of the Cascadia Root arc by the Pacific Northwest along with accretion of the Siletzia and Pacific Rim terranes
45.
Neogene
–
The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene, some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. During this period, mammals and birds continued to evolve into modern forms. Early hominids, the ancestors of humans, appeared in Africa near the end of the period, some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the ocean currents from the Pacific to the Atlantic ocean. The global climate cooled considerably over the course of the Neogene, the terms Neogene System and upper Tertiary System describe the rocks deposited during the Neogene Period. The continents in the Neogene were very close to their current positions, the Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas, sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America. The global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began, marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the part of the period. Mammals and birds continued to be the dominant terrestrial vertebrates, the first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones, grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison. The Neogene traditionally ended at the end of the Pliocene Epoch, just before the definition of the beginning of the Quaternary Period. However, there was a movement amongst geologists to also include ongoing geological time in the Neogene, by dividing the Cenozoic Era into three periods instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras. The International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene, with a date of 2.58 Ma. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs, thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya. Digital Atlas of Neogene Life for the Southeastern United States — by San Jose State University via Web Archive
46.
Seafloor spreading ridge
–
A mid-ocean ridge is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a known as a rift running along its spine. This type of mountain ridge is characteristic of what is known as an oceanic spreading center. The production of new results from mantle upwelling in response to plate spreading. The buoyant melt rises as magma at a linear weakness in the oceanic crust, a mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary. Mid-ocean ridges are geologically active, with new magma constantly emerging onto the floor and into the crust at. The crystallized magma forms new crust of basalt and gabbro and they are formed by two oceanic plates moving away from each other. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis, new magma of basalt composition emerges at and near the axis because of decompression melting in the underlying Earths mantle. The oceanic crust is made up of much younger than the Earth itself. Most oceanic crust in the basins is less than 200 million years old. The crust is in a constant state of renewal at the ocean ridges, moving away from the mid-ocean ridge, ocean depth progressively increases, the greatest depths are in ocean trenches. As the oceanic crust moves away from the axis, the peridotite in the underlying mantle cools. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere, by contrast, fast spreading ridges like the East Pacific Rise are narrow, sharp incisions surrounded by generally flat topography that slopes away from the ridge over many hundreds of miles. The overall shape of ridges results from Pratt isostacy, close to the ridge there is hot. As the oceanic plates cool, away from the axes, the oceanic mantle lithosphere thickens. Thus older seafloor is underlain by denser material and sits lower, there are two processes, ridge-push and slab pull, thought to be responsible for the spreading seen at mid-ocean ridges, and there is some uncertainty as to which is dominant. Ridge-push occurs when the bulk of the ridge pushes the rest of the tectonic plate away from the ridge. At the subduction zone, slab-pull comes into effect and this is simply the weight of the tectonic plate being subducted below the overlying plate dragging the rest of the plate along behind it
