Gulf of California
The Gulf of California is a marginal sea of the Pacific Ocean that separates the Baja California Peninsula from the Mexican mainland. It is bordered by the states of Baja California, Baja California Sur and Sinaloa with a coastline of 4,000 km. Rivers which flow into the Gulf of California include the Colorado, Mayo, Sinaloa and the Yaqui; the gulf's surface area is about 160,000 km2. Depths range from fording at the estuary near Yuma, Arizona, to in excess of 3,000 meters in the deepest parts; the Gulf is thought to be one of the most diverse seas on the planet, is home to more than 5,000 species of micro-invertebrates. Home to over a million people, Baja California is the second-longest peninsula in the world, after the Malay Peninsula in Southeast Asia. Parts of the Gulf of California are a UNESCO World Heritage Site. AreaThe International Hydrographic Organization defines the southern limit of the Gulf of California as: "A line joining Piastla Point in Mexico, 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 mean depth of 818.08 m, a volume of 145,000 km3. The Gulf of California includes three faunal regions: the Northern Gulf of California the Central Gulf of California the Southern Gulf of CaliforniaOne recognized transition zone is termed the Southwestern Baja California Peninsula. Transition zones exist between faunal regions, they vary for each individual species. Geology Geologic evidence is interpreted by geologists as indicating the Gulf of California came into being around 5.3 million years ago as tectonic forces rifted the Baja California Peninsula off the North American Plate. As part of this process, the East Pacific Rise propagated up the middle of the Gulf along the seabed; this extension of the East Pacific Rise is referred to as the Gulf of California Rift Zone. The Gulf would extend as far as Indio, except for the tremendous delta created by the Colorado River; this delta blocks the sea from flooding the Imperial Valleys.
Volcanism dominates the East Pacific Rise. The island of Isla Tortuga is one example of this 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, Baja California Sur. Islands The Gulf of California contains 37 major islands – the two largest being Isla Ángel de la Guarda and Tiburón Island. Most of the islands are found on the peninsular side of the gulf. In fact, many of the islands of the Sea of Cortez are the result of volcanic explosions that occurred during the early history of Baja California; the islands of Islas Marías, Islas San Francisco, Isla Partida are thought to be the result of such explosions. The formations of the islands, are not dependent on each other, they were each formed as a result of an individual structural occurrence. Several islands, including Isla Coronados, are home to volcanoes; the gulf has islands which together total about 420 hectares.
All of them as a whole were enacted as "Area Reserve and Migratory Bird Refuge and Wildlife" on August 2, 1978. In June 2000, the islands were given a new category "Protection Area Wildlife". In addition to this effort by the Mexican government, for its importance and recognition worldwide, all islands in the Gulf of California are part of the international program "Man and Biosphere" and are part of the World Reserve Network UNESCO Biosphere as Special Biosphere Reserve. Due to the vast expanse covered by this federal protected area conservation and management is carried out through a system of four regional directorates by way of co-direction. There is a regional directorate in the states of Baja California, Baja California Sur and Sinaloa. Notwithstanding the foregoing, the work of direct and indirect conservation is done in the islands is governed by a single Management Program, published in 2000, complemented by local and specific management programs archipelagos; the Directorate of Protection Area Wildlife California Gulf Islands in Baja California is responsible for 56 islands located off the coast of the state.
These are grouped into four archipelagos: San Luis Gonzaga or Enchanted, Guardian Angel, Bahia de los Angeles and San Lorenzo. Shores and tidesThe three general types of shores found in the Gulf of California include rocky shore, sandy beach, tidal flat; some of the rich biodiversity and high endemism that characterize the Gulf of California and make it such a hotspot for fishing can be attributed to insignificant factors, such as the types of rocks that make up a shore. Beaches with softer, more porous rocks have a higher species richness than those with harder, smoother rocks. Porous rocks will have more cracks and crevices in them, making them ideal living spaces for many animals; the rocks themselves, however need to be stable on the shore for a habitat to be stable. Additionally, the color of the rocks can affect the organisms living on a shore. For example, darker rocks will be warmer than lighter ones, can deter animals that do not have a high tolerance for heat. The
Wyoming is a state in the mountain region of the western United States. The state is the 10th largest by area, the least populous, the second most sparsely populated state in the country. Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, on the west by Idaho and Montana; the state population was estimated at 577,737 in 2018, less than 31 of the most populous U. S. cities including Denver in neighboring Colorado. Cheyenne is the state capital and the most populous city, with an estimated population of 63,624 in 2017; the western two-thirds of the state is covered by the mountain ranges and rangelands of the Rocky Mountains, while the eastern third of the state is high elevation prairie called the High Plains. Half of the land in Wyoming is owned by the U. S. government, leading Wyoming to rank sixth by area and fifth by proportion of a state's land owned by the federal government. Federal lands include two national parks—Grand Teton and Yellowstone—two national recreation areas, two national monuments, several national forests, historic sites, fish hatcheries, wildlife refuges.
Original inhabitants of the region include the Crow, Arapaho and Shoshone. Southwestern Wyoming was in the Spanish Empire and Mexican territory until it was ceded to the United States in 1848 at the end of the Mexican–American War; the region acquired the name Wyoming when a bill was introduced to the U. S. Congress in 1865 to provide a "temporary government for the territory of Wyoming"; the name was used earlier for the Wyoming Valley in Pennsylvania, is derived from the Munsee word xwé:wamənk, meaning "at the big river flat". The main drivers of Wyoming's economy are mineral extraction—mostly coal, natural gas, trona—and tourism. Agricultural commodities include livestock, sugar beets and wool; the climate is semi-arid and continental and windier than the rest of the U. S. with greater temperature extremes. Wyoming has been a politically conservative state since the 1950s, with the Republican Party candidate winning every presidential election except 1964. Wyoming's climate is semi-arid and continental, is drier and windier in comparison to most of the United States with greater temperature extremes.
Much of this is due to the topography of the state. Summers in Wyoming are warm with July high temperatures averaging between 85 and 95 °F in most of the state. With increasing elevation, this average drops with locations above 9,000 feet averaging around 70 °F. Summer nights throughout the state are characterized by a rapid cooldown with the hottest locations averaging in the 50–60 °F range at night. In most of the state, most of the precipitation tends to fall in early summer. Winters are cold, but are variable with periods of sometimes extreme cold interspersed between mild periods, with Chinook winds providing unusually warm temperatures in some locations. Wyoming is a dry state with much of the land receiving less than 10 inches of rainfall per year. Precipitation depends on elevation with lower areas in the Big Horn Basin averaging 5–8 inches; the lower areas in the North and on the eastern plains average around 10–12 inches, making the climate there semi-arid. Some mountain areas do receive a good amount of precipitation, 20 inches or more, much of it as snow, sometimes 200 inches or more annually.
The state's highest recorded temperature is 114 °F at Basin on July 12, 1900 and the lowest recorded temperature is −66 °F at Riverside on February 9, 1933. The number of thunderstorm days vary across the state with the southeastern plains of the state having the most days of thunderstorm activity. Thunderstorm activity in the state is highest during early summer; the southeastern corner of the state is the most vulnerable part of the state to tornado activity. Moving away from that point and westwards, the incidence of tornadoes drops with the west part of the state showing little vulnerability. Tornadoes, where they occur, tend to be small and brief, unlike some of those that occur farther east; as specified in the designating legislation for the Territory of Wyoming, Wyoming's borders are lines of latitude 41°N and 45°N, longitude 104°3'W and 111°3'W, making the shape of the state a latitude-longitude quadrangle. Wyoming is one of only three states to have borders along only straight latitudinal and longitudinal lines, rather than being defined by natural landmarks.
Due to surveying inaccuracies during the 19th century, Wyoming's legal border deviates from the true latitude and longitude lines by up to half of a mile in some spots in the mountainous region along the 45th parallel. Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, on the west by Idaho, it is the tenth largest state in the United States in total area, containing 97,814 square miles and is made up of 23 counties. From the north border to the south border it is 276 miles; the Great Plains meet the Rocky Mountains in Wyoming. The state is a great plateau broken by many mountain ranges. Surface elevations range from the summit of Gannett Peak in the Wind River Mountain Range, at 13,804 feet, to the Belle Fourche River val
Glen Canyon is a natural canyon in southeastern and south-central Utah. A small part of the lower end of Glen Canyon extends into the northern part of Arizona and terminates at the Vermilion Cliffs area in the United States. Like the Grand Canyon to the south, Glen Canyon is part of the immense system of canyons carved by the Colorado River and its tributaries. In 1963, a reservoir, Lake Powell, was created by the construction of the Glen Canyon Dam, in the Arizona portion of Glen Canyon; this dam backed water into Utah. Lake Powell was not the result of negotiations over the controversial damming of the Green River within Dinosaur National Monument at Echo Park; the Echo Park Dam proposal was abandoned due to country wide citizen pressure on Congress to do so. Glen Canyon dam remains a central issue for modern environmentalist movements. Beginning in the late 1990s, the Sierra Club and other organizations renewed the call to dismantle the dam and drain Lake Powell in Lower Glen Canyon. Today, Glen Canyon and Lake Powell are managed by the U.
S. Department of the Interior within Glen Canyon National Recreation Area. Around 1956, archaeologists and biologists from the University of Utah and the Museum of Northern Arizona, using National Park research grants, planned an emergency excavation of Lower Glen Canyon, soon to be flooded by the new Glen Canyon Dam. Between 1958 and 1960, four investigative phases, combined with other surveys prior to 1957, discovered 250 archaeological sites within the canyon; the Lower Glen Canyon survey was completed in 1958. Excavations began during the summer of 1958 on 16 sites. A thesis emerged that prehistoric people living permanently on the highlands south of Glen Canyon, on the Cummings Mesa, farmed the Lower Glen Canyon on a seasonal basis, gathered raw materials. To prove this thesis of seasonal habitation, criteria such as architectural units, locations of trail systems, occurrence of ceremonial structures, prevalence of burials, position of natural and cultural strata. Four types of sites are described in the survey classified as either open sites situated on rock terraces.
Open sites are the majority on both sides of the river. The majority of sites Navajo camps, feature lithic garbage or ceramics, or both. Talus sites are recorded. Most of the cultural remains found are chipped stone tools, including projectile points, drills, knives and ground stone tools and manos; the collection of sherds are Tusayan Gray Ware and Tusayan White Ware. Petroglyph panels are found throughout Glen Canyon. "Pecked and incised figures depict mountain sheep, human figures, human handprints and animal tracks. Geometric figures range from circles and spirals to complex rectilinear patterns; the human figures have triangular bodies. Painted figures have been reported for both sides of the river.... Petroglyph panels of such quality are lacking from the highland regions adjacent to Glen Canyon". Studies indicate a chronology for the Lower Glen Canyon prehistory, "from pre-A. D. 1 to the 15th century and recorded history from 1776 to the present". A Late Basketmaker II Era is represented by several sites.
Radiocarbon dates from charcoal material are from A. D. 250 to 440. Basketmaker III is not found in the Lower Glen Canyon, but is documented in Navajo Canyon, a large left bank tributary of the Colorado River, within the geographical area of the Lower Glen Canyon. Basketmaker III introduces fired pottery Lino Black-on-gray and Lino Gray, some small amounts of Lino Fugitive Red and Obelisk Gray; the Basketmaker culture is believed to have lasted than Pueblo I. Pueblo I Era remains are found at Rock Creek in Lower Glen Canyon, in Navajo Canyon; the pottery types are Kana-a Black-on-white, Deadmans Black-on-red, Kana-a Gray, made from deposits found in Lizard Alcove. Pueblo I is the best documented period of Navajo Canyon, beginning in 800 A. D, lasting 200 years. "Pueblo II in Navajo Canyon is represented by the absence of Kana-a Black-on-white and the dominance of Black Mesa Black-on-white". Pueblo II and early Pueblo III is the best documented cultural area in Lower Glen Canyon corresponding with habitation on Cummings Mesa.
Pottery includes Tusayan varieties, Black-on-white, Black-on-red, Red Wear Polychromes. Hopi people from the Jeddito area came into the canyons in the 14th century, represented by Yellow Wares Jeddito Black-on-yellow, Jeddito plain. Most of the ceramic material found in the main canyon was made in the highlands, although it is possible some pottery was manufactured in Lower Glen Canyon. Clay deposits are found along the river, some crude pottery specimens, that may have been made there. Only four burials were found in Lower Glen Canyon at three sites. Trash dumps are not common at most sites; this is more evidence to suggest the seasonal occupation of farmers. Cultural similarities are based on the absence, of certain types of ceramic wares. Group types of pottery including Kayenta, with Fremont, Mesa Verde or Anasazi types of White and Desert Gray Ware were found on the right bank of the Colorado. Basketmaker II is characterized by a lack of pottery, as well as above ground and underground cists lined with slabs.
There is little evidence of permanent occupation except at Talus Ruin, a small pueblo with a kiva, a
The Alamo River flows west and north from the Mexicali Valley across the Imperial Valley. The 52-mile-long river drains into the Salton Sea; the New River, Alamo River, Salton Sea of the 21st century started in autumn 1904, when the Colorado River, swollen by seasonal rainfall and snow-melt, flowed through a series of three human-engineered openings in the constructed levee bank of the Alamo Canal. The resulting flood breached an Imperial Valley dike; the sudden influx of water and the lack of any drainage from the basin resulted in the formation of the Salton Sea. It took less than two years to control the Colorado River’s inflow to the Alamo Canal and stop the uncontrolled flooding of the Salton Sink, but the canal was channelized with operational headgates by the early part of 1907; the Alamo and New Rivers at a lesser rate. The river was named after the Spanish name for the Fremont cottonwood. In most places, the river is a vegetation-choked ravine with a small watercourse at the bottom; the California Office of Environmental Health Hazard Assessment has issued a safe eating advisory based on mercury, DDTs, PCBs, selenium.
Lake Cahuilla Salton Sea Tributaries of the Salton Sea
Lower Colorado River Valley
The Lower Colorado River Valley is the river region of the lower Colorado River of the southwestern United States in North America that rises in the Rocky Mountains and has its outlet at the Colorado River Delta in the northern Gulf of California in northwestern Mexico, between the states of Baja California and Sonora. This north–south stretch of the Colorado River forms the border between the U. S. states of California/Arizona and Nevada/Arizona, between the Mexican states of Baja California/Sonora. It is defined as the region from below Hoover Dam and Lake Mead to its outlet at the northern Gulf of California, it is home to recreation activities from the river, the lakes created by dams and the home of various cities and towns along the river, or associated with the valley region. Five Indian reservations are located in the LCRV: the Chemehuevi, Fort Mojave and Colorado River Indian Reservations; some of the highest absolute air temperatures are recorded in the LCRV. Worldwide, only some deserts found in Africa and in the Middle East stand up with an hotter summer climate on average.
The LCRV is defined by three deserts. The Mojave Desert is in southeast California, southern Nevada, northwest Arizona. To the south is the Sonoran Desert on both sides of the Colorado River; however an ecozone delineation occurs in the transition from Arizona to southeast California. The Lower Colorado River Valley is located in the north, northwestern Sonoran Desert; the LCRV extends about 350 miles from Hoover Dam to the Colorado River Delta. The Sonoran Desert itself is more than twice as extensive north-to-south, about 450 miles in width. Two species, Desert Ironwood- and the Lesser Long-nosed Bat, have geographic ranges identical to the Sonoran Desert, are indicator species of the Sonoran Desert region; the spring flowering of Ironwood, the bat species migration arrivals become indicators of annual or multi-year climate trends for regions of the Sonoran Desert. The Lower Colorado River Valley subregion of the Sonoran Desert bioregion has multiple threats; some major threats include urbanization, clearing of land for agriculture, human occupancy – as a result of imported external resources, camping and camptrailers on BLM land.
Other threats include harvesting for fuelwood, etc. of desert ironwood, Olneya tesota, destruction of land by offroad vehicles in sand dunes, harvesting and manipulation of groundwater. Laughlin, Nevada in Clark County, Nevada Needles, California in San Bernardino County Bullhead City, Arizona Mojave Valley, Arizona Lake Havasu City, Arizona Vidal, California Parker, Arizona Blythe, California Quartzite, Arizona Winterhaven, California in Imperial County, California Yuma, Arizona in Yuma County, Arizona San Luis, Arizona San Luis Río Colorado, Sonora Rio Grande, the eastern river valley drainage of the Southwest USA Rio Grande Valley Category:Rio Grande Category:Fauna of the U. S. Rio Grande Valleys List of dams of the LCRV List of LCRV communities Little. Atlas of United States Trees, Volume 3, Minor Western Hardwoods, Elbert L, 1976, US Government Printing Office. Library of Congress No. 79-653298. Map 103, Olneya tesota. Journey of the Nectar Bats Map, Lesser Long-nosed Bat range. US Bureau of Reclamation, "Dams Along the Lower Colorado River"
Colorado is a state of the Western United States encompassing most of the southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. It is the 8th most extensive and 21st most populous U. S. state. The estimated population of Colorado was 5,695,564 on July 1, 2018, an increase of 13.25% since the 2010 United States Census. The state was named for the Colorado River, which early Spanish explorers named the Río Colorado for the ruddy silt the river carried from the mountains; the Territory of Colorado was organized on February 28, 1861, on August 1, 1876, U. S. President Ulysses S. Grant signed Proclamation 230 admitting Colorado to the Union as the 38th state. Colorado is nicknamed the "Centennial State" because it became a state one century after the signing of the United States Declaration of Independence. Colorado is bordered by Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, Utah to the west, touches Arizona to the southwest at the Four Corners.
Colorado is noted for its vivid landscape of mountains, high plains, canyons, plateaus and desert lands. Colorado is part of the western and southwestern United States, is one of the Mountain States. Denver is most populous city of Colorado. Residents of the state are known as Coloradans, although the antiquated term "Coloradoan" is used. Colorado is notable for its diverse geography, which includes alpine mountains, high plains, deserts with huge sand dunes, deep canyons. In 1861, the United States Congress defined the boundaries of the new Territory of Colorado by lines of latitude and longitude, stretching from 37°N to 41°N latitude, from 102°02'48"W to 109°02'48"W longitude. After 158 years of government surveys, the borders of Colorado are now defined by 697 boundary markers and 697 straight boundary lines. Colorado and Utah are the only states that have their borders defined by straight boundary lines with no natural features; the southwest corner of Colorado is the Four Corners Monument at 36°59'56"N, 109°2'43"W.
This is the only place in the United States where four states meet: Colorado, New Mexico and Utah. The summit of Mount Elbert at 14,440 feet elevation in Lake County is the highest point in Colorado and the Rocky Mountains of North America. Colorado is the only U. S. state that lies above 1,000 meters elevation. The point where the Arikaree River flows out of Yuma County and into Cheyenne County, Kansas, is the lowest point in Colorado at 3,317 feet elevation; this point, which holds the distinction of being the highest low elevation point of any state, is higher than the high elevation points of 18 states and the District of Columbia. A little less than half of Colorado is flat and rolling land. East of the Rocky Mountains are the Colorado Eastern Plains of the High Plains, the section of the Great Plains within Nebraska at elevations ranging from 3,350 to 7,500 feet; the Colorado plains are prairies but include deciduous forests and canyons. Precipitation averages 15 to 25 inches annually. Eastern Colorado is presently farmland and rangeland, along with small farming villages and towns.
Corn, hay and oats are all typical crops. Most villages and towns in this region boast both a grain elevator. Irrigation water is available from subterranean sources. Surface water sources include the South Platte, the Arkansas River, a few other streams. Subterranean water is accessed through artesian wells. Heavy use of wells for irrigation caused underground water reserves to decline. Eastern Colorado hosts considerable livestock, such as hog farms. 70% of Colorado's population resides along the eastern edge of the Rocky Mountains in the Front Range Urban Corridor between Cheyenne and Pueblo, Colorado. This region is protected from prevailing storms that blow in from the Pacific Ocean region by the high Rockies in the middle of Colorado; the "Front Range" includes Denver, Fort Collins, Castle Rock, Colorado Springs, Pueblo and other townships and municipalities in between. On the other side of the Rockies, the significant population centers in Western Colorado are the cities of Grand Junction and Montrose.
The Continental Divide of the Americas extends along the crest of the Rocky Mountains. The area of Colorado to the west of the Continental Divide is called the Western Slope of Colorado. West of the Continental Divide, water flows to the southwest via the Colorado River and the Green River into the Gulf of California. Within the interior of the Rocky Mountains are several large parks which are high broad basins. In the north, on the east side of the Continental Divide is the North Park of Colorado; the North Park is drained by the North Platte River, which flows north into Nebraska. Just to the south of North Park, but on the western side of the Continental Divide, is the Middle Park of Colorado, drained by the Colorado River; the South Park of Colorado is the region of the headwaters of the South Platte River. In southmost Colorado is the large San Luis Valley, where the headwaters of the Rio Grande are located; the valley sits between the Sangre De Cristo Mountains and San Juan Mountains, consists of large desert lands that run into the mountains.
The Rio Grande drains due south into New Mexico and Texas. Across the Sangre de Cristo Range to the east of the S
The Rocky Mountains known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch more than 4,800 kilometers from the northernmost part of British Columbia, in western Canada, to New Mexico in the Southwestern United States. Located within the North American Cordillera, the Rockies are somewhat distinct from the Pacific Coast Ranges, Cascade Range, the Sierra Nevada, which all lie farther to the west; the Rocky Mountains formed 80 million to 55 million years ago during the Laramide orogeny, in which a number of plates began sliding underneath the North American plate. The angle of subduction was shallow, resulting in a broad belt of mountains running down western North America. Since further tectonic activity and erosion by glaciers have sculpted the Rockies into dramatic peaks and valleys. At the end of the last ice age, humans began inhabiting the mountain range. After Europeans, such as Sir Alexander Mackenzie, Americans, such as the Lewis and Clark expedition, began exploring the range and furs drove the initial economic exploitation of the mountains, although the range itself never experienced dense population.
Public parks and forest lands protect much of the mountain range, they are popular tourist destinations for hiking, mountaineering, hunting, mountain biking and snowboarding. The name of the mountains is a translation of an Amerindian name, related to Algonquian; the first mention of their present name by a European was in the journal of Jacques Legardeur de Saint-Pierre in 1752, where they were called "Montagnes de Roche". The Rocky Mountains are defined as stretching from the Liard River in British Columbia south to the Rio Grande in New Mexico; the Rockies vary in width from 110 to 480 kilometres. The Rocky Mountains are notable for containing the highest peaks in central North America; the range's highest peak is Mount Elbert located in Colorado at 4,401 metres above sea level. Mount Robson in British Columbia, at 3,954 metres, is the highest peak in the Canadian Rockies; the eastern edge of the Rockies rises above the Interior Plains of central North America, including the Sangre de Cristo Mountains of New Mexico and Colorado, the Front Range of Colorado, the Wind River Range and Big Horn Mountains of Wyoming, the Absaroka-Beartooth ranges and Rocky Mountain Front of Montana and the Clark Range of Alberta.
The western edge of the Rockies includes ranges such as the Wasatch near Salt Lake City and the Bitterroots along the Idaho-Montana border. The Great Basin and Columbia River Plateau separate these subranges from distinct ranges further to the west. In Canada, the western edge of the Rockies is formed by the huge Rocky Mountain Trench, which runs the length of British Columbia from its beginnings in the middle Flathead River valley in western Montana to the south bank of the Liard River. Geographers define three main groups of the Canadian Rockies: the Continental Ranges, Hart Ranges, Muskwa Ranges; the Rockies do not extend into central British Columbia. Other mountain ranges continue beyond the Liard River, including the Selwyn Mountains in Yukon, the Brooks Range in Alaska, but those are not part of the Rockies, though they are part of the American Cordillera; the Continental Divide of the Americas is located in the Rocky Mountains and designates the line at which waters flow either to the Atlantic or Pacific Oceans.
Triple Divide Peak in Glacier National Park is so named because water falling on the mountain reaches not only the Atlantic and Pacific but Hudson Bay as well. Farther north in Alberta, the Athabasca and other rivers feed the basin of the Mackenzie River, which has its outlet on the Beaufort Sea of the Arctic Ocean. Human population is not dense in the Rocky Mountains, with an average of four people per square kilometer and few cities with over 50,000 people. However, the human population grew in the Rocky Mountain states between 1950 and 1990; the forty-year statewide increases in population range from 35% in Montana to about 150% in Utah and Colorado. The populations of several mountain towns and communities have doubled in the last forty years. Jackson, increased 260%, from 1,244 to 4,472 residents, in forty years; the rocks in the Rocky Mountains were formed. The oldest rock is Precambrian metamorphic rock. There is Precambrian sedimentary argillite, dating back to 1.7 billion years ago. During the Paleozoic, western North America lay underneath a shallow sea, which deposited many kilometers of limestone and dolomite.
In the southern Rocky Mountains, near present-day Colorado, these ancestral rocks were disturbed by mountain building 300 Ma, during the Pennsylvanian. This mountain-building produced the Ancestral Rocky Mountains, they consisted of Precambrian metamorphic rock forced upward through layers of the limestone laid down in the shallow sea. The mountains eroded throughout the late Paleozoic and early Mesozoic, leaving extensive deposits of sedimentary rock. Terranes began colliding with the western edge of North America in the Mississippian, causing the Antler orogeny. For 270 million years, the focus of the effects of plate collisions were near the edge of the North American plate boundary, far to the west of the Rocky Mountain region, it was. The current Rocky Mountains arose in the Laramide orogeny from between 55 Ma. For the Canadi