A mountain range or hill range is a series of mountains or hills ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form and alignment that have arisen from the same cause an orogeny. Mountain ranges are formed by a variety of geological processes, but most of the significant ones on Earth are the result of plate tectonics. Mountain ranges are found on many planetary mass objects in the Solar System and are a feature of most terrestrial planets. Mountain ranges are segmented by highlands or mountain passes and valleys. Individual mountains within the same mountain range do not have the same geologic structure or petrology, they may be a mix of different orogenic expressions and terranes, for example thrust sheets, uplifted blocks, fold mountains, volcanic landforms resulting in a variety of rock types. Most geologically young mountain ranges on the Earth's land surface are associated with either the Pacific Ring of Fire or the Alpide Belt.
The Pacific Ring of Fire includes the Andes of South America, extends through the North American Cordillera along the Pacific Coast, the Aleutian Range, on through Kamchatka, Taiwan, the Philippines, Papua New Guinea, to New Zealand. The Andes is 7,000 kilometres long and is considered the world's longest mountain system; the Alpide belt includes Indonesia and Southeast Asia, through the Himalaya, Caucasus Mountains, Balkan Mountains fold mountain range, the Alps, ends in the Spanish mountains and the Atlas Mountains. The belt includes other European and Asian mountain ranges; the Himalayas contain the highest mountains in the world, including Mount Everest, 8,848 metres high and traverses the border between China and Nepal. Mountain ranges outside these two systems include the Arctic Cordillera, the Urals, the Appalachians, the Scandinavian Mountains, the Great Dividing Range, the Altai Mountains and the Hijaz Mountains. If the definition of a mountain range is stretched to include underwater mountains the Ocean Ridges form the longest continuous mountain system on Earth, with a length of 65,000 kilometres.
The mountain systems of the earth are characterized by a tree structure, where mountain ranges can contain sub-ranges. The sub-range relationship is expressed as a parent-child relationship. For example, the White Mountains of New Hampshire and the Blue Ridge Mountains are sub-ranges of the Appalachian Mountains. Equivalently, the Appalachians are the parent of the White Mountains and Blue Ridge Mountains, the White Mountains and the Blue Ridge Mountains are children of the Appalachians; the parent-child expression extends to the sub-ranges themselves: the Sandwich Range and the Presidential Range are children of the White Mountains, while the Presidential Range is parent to the Northern Presidential Range and Southern Presidential Range. The position of mountains influences climate, such as snow; when air masses move up and over mountains, the air cools producing orographic precipitation. As the air descends on the leeward side, it warms again and is drier, having been stripped of much of its moisture.
A rain shadow will affect the leeward side of a range. Mountain ranges are subjected to erosional forces which work to tear them down; the basins adjacent to an eroding mountain range are filled with sediments which are buried and turned into sedimentary rock. Erosion is at work while the mountains are being uplifted until the mountains are reduced to low hills and plains; the early Cenozoic uplift of the Rocky Mountains of Colorado provides an example. As the uplift was occurring some 10,000 feet of Mesozoic sedimentary strata were removed by erosion over the core of the mountain range and spread as sand and clays across the Great Plains to the east; this mass of rock was removed as the range was undergoing uplift. The removal of such a mass from the core of the range most caused further uplift as the region adjusted isostatically in response to the removed weight. Rivers are traditionally believed to be the principal cause of mountain range erosion, by cutting into bedrock and transporting sediment.
Computer simulation has shown that as mountain belts change from tectonically active to inactive, the rate of erosion drops because there are fewer abrasive particles in the water and fewer landslides. Mountains on other planets and natural satellites of the Solar System are isolated and formed by processes such as impacts, though there are examples of mountain ranges somewhat similar to those on Earth. Saturn's moon Titan and Pluto, in particular exhibit large mountain ranges in chains composed of ices rather than rock. Examples include the Mithrim Montes and Doom Mons on Titan, Tenzing Montes and Hillary Montes on Pluto; some terrestrial planets other than Earth exhibit rocky mountain ranges, such as Maxwell Montes on Venus taller than any on Earth and Tartarus Montes on Mars, Jupiter's moon Io has mountain ranges formed from tectonic processes including Boösaule Montes, Dorian Montes, Hi'iaka Montes and Euboea Montes. Peakbagger Ranges Home Page Bivouac.com
Geographic Names Information System
The Geographic Names Information System is a database that contains name and locative information about more than two million physical and cultural features located throughout the United States of America and its territories. It is a type of gazetteer. GNIS was developed by the United States Geological Survey in cooperation with the United States Board on Geographic Names to promote the standardization of feature names; the database is part of a system that includes bibliographic references. The names of books and historic maps that confirm the feature or place name are cited. Variant names, alternatives to official federal names for a feature, are recorded; each feature receives a permanent, unique feature record identifier, sometimes called the GNIS identifier. The database never removes an entry, "except in cases of obvious duplication." The GNIS accepts proposals for new or changed names for U. S. geographical features. The general public can make proposals at the GNIS web site and can review the justifications and supporters of the proposals.
The Bureau of the Census defines Census Designated Places as a subset of locations in the National Geographic Names Database. U. S. Postal Service Publication 28 gives standards for addressing mail. In this publication, the postal service defines two-letter state abbreviations, street identifiers such as boulevard and street, secondary identifiers such as suite. Canadian Geographical Names Data Base, a similar, but non-public-domain, database for locations within Canada only GEOnet Names Server, a similar database for locations outside the United States United Nations Conference on the Standardization of Geographical Names U. S. Department of the Interior, U. S. Geological Survey, National Mapping Division, Digital Gazeteer: Users Manual. Least Heat Moon, Blue Highways: A Journey Into America. ISBN 0-316-35329-9 Jouris, All Over The Map, ISBN 0-89815-649-1 Report: "Countries, Areas of Special Sovereignty, Their Principal Administrative Divisions," Federal Information Processing Standards, FIPS 10-4.
Standard was withdrawn in September 2008, See Federal Register Notice: Vol. 73, No. 170, page 51276 Report: "Principles and Procedures: Domestic Geographic Names," U. S. Board on Geographic Names, 1997. U. S. Postal Service Publication 28. U. S. Board on Geographic Names website Geographic Names Information System Proposals from the general public Meeting minutes
Joshua Tree National Park
Joshua Tree National Park is an American national park in southeastern California, east of Los Angeles, near San Bernardino and Palm Springs. The park is named for the Joshua trees native to the Mojave Desert. Declared a national monument in 1936, Joshua Tree was redesignated as a national park in 1994 when the U. S. Congress passed the California Desert Protection Act. Encompassing a total of 790,636 acres —an area larger than the state of Rhode Island—the park includes 429,690 acres of designated wilderness. Straddling the border between San Bernardino County and Riverside County, the park includes parts of two deserts, each an ecosystem whose characteristics are determined by elevation: the higher Mojave Desert and the lower Colorado Desert; the Little San Bernardino Mountains traverse the southwest edge of the park. The earliest known residents of the land in and around what became Joshua Tree National Park were the people of the Pinto Culture, who lived and hunted here between 8000 and 4000 BCE.
Their stone tools and spear points, discovered in the Pinto Basin in the 1930s, suggest that they hunted game and gathered seasonal plants, but little else is known about them. Residents included the Serrano, the Cahuilla, the Chemehuevi peoples. All three lived at times in small villages in or near water the Oasis of Mara in what non-aboriginals called Twentynine Palms, they were hunter-gatherers who subsisted on plant foods supplemented by small game and reptiles while using other plants for making medicines and arrows, other articles of daily life. A fourth group, the Mojaves, used the local resources as they traveled along trails between the Colorado River and the Pacific coast. In the 21st century, small numbers of all four peoples live in the region near the park. In 1772, a group of Spaniards led by Pedro Fages, made the first European sightings of Joshua trees while pursuing native converts to Christianity who had run away from a mission in San Diego. By 1823, the year Mexico achieved independence from Spain, a Mexican expedition from Los Angeles, in what was Alta California, is thought to have explored as far east as the Eagle Mountains in what became the park.
Three years Jedediah Smith led a group of American fur trappers and explorers along the nearby Mojave Trail, others soon followed. Two decades after that, the United States defeated Mexico in the Mexican–American War and took over about half of Mexico's original territory, including California and the future parkland. In 1870, white settlers began grazing cattle on the tall grasses. In 1888, a gang of cattle rustlers moved into the region near the Oasis of Mara. Led by brothers James. B. and William S. McHaney, they hid stolen cattle in a box canyon at Cow Camp. Throughout the region, ranchers dug wells and built rainwater catchments called "tanks", such as White Tank and Barker Dam. In 1900, C. O. Barker, a miner and cattleman, built the original Barker Dam improved by William "Bill" Keys, a rancher. Grazing continued in the park through 1945. Barker Dam was added to the National Register of Historic Places in 1975. Between the 1860s and the 1940s, miners worked about 300 pit mines small, in what became the park.
The most successful, the Lost Horse Mine, produced gold and silver worth about $5 million in today's currency. Johnny Lang and others, the original owners of the Lost Horse Mine, installed a two-stamp mill to process ore at the site, the next owner, J. D. Ryan, replaced it with a 10-stamp steam-powered mill. Ryan pumped water from his ranch to the mill and cut timber from the nearby hills to heat water to make steam. Most of the structures associated with the mine fell apart, for safety reasons the National Park Service plugged the mine, which had collapsed; the Desert Queen Mine on Keys' Desert Queen Ranch was another productive gold mine. In the early 1930s, Keys bought a gasoline-powered two-stamp mill, the Wall Street Mill, moved it to his ranch to process ore; the ranch and mill were added to the NRHP in 1975 and the mine in 1976. Some of the mines in the park yielded copper and iron. On August 10, 1936, after Minerva Hoyt and others persuaded the state and federal governments to protect the area, president Franklin D. Roosevelt used the power of the 1906 Antiquities Act to establish Joshua Tree National Monument, protecting about 825,000 acres.
In 1950, the size of the park was reduced by about 290,000 acres to open the land to more mining. The monument was redesignated as a national park on October 31, 1994, by the Desert Protection Act, which added 234,000 acres. In 2019, the park expanded by 4,518 acres under a bill included in the John D. Dingell, Jr. Conservation and Recreation Act; the higher and cooler Mojave Desert is the special habitat of Yucca brevifolia, the Joshua tree for which the park is named. It occurs in patterns from dense forests to distantly spaced specimens. In addition to Joshua tree forests, the western part of the park includes some of the most interesting geologic displays found in California's deserts; the dominant geologic features of this landscape are hills of bare rock broken up into loose boulders. These hills are popular among rock scrambling enthusiasts; the flatland between these hills is sparsely forested with Joshua trees. Together with the boulder piles and Skull Rock, the trees make the landscape otherworldly.
Temperatures are most comfortable
San Gorgonio Mountain
San Gorgonio Mountain known locally as Mount San Gorgonio, or Old Greyback, is the highest peak in Southern California and the Transverse Ranges at 11,503 feet. It is in the San Bernardino Mountains, 27 miles east of the city of San Bernardino and 12 miles north-northeast of San Gorgonio Pass, it lies within the San Gorgonio Wilderness, part of the Sand to Snow National Monument managed by the San Bernardino National Forest. Spanish missionaries in the area during the early 17th century named the peak after Saint Gorgonius. Since it is the highest point in a region, separated from higher peaks by low terrain, San Gorgonio Mountain is one of the most topographically prominent peaks in the United States, it is ranked 7th among peaks in 18th among overall. Like other high peaks in the Transverse Ranges, the mountain has a pyramid shape, with a steep north face and a shallower south face; the mountain is broad. In contrast to its spectacular but lower neighbor, San Jacinto Peak, San Gorgonio is not craggy, from a distance, it only appears to be an high hill, earning it the name of greyback.
Despite not being striking in appearance during the summer, it is the only mountain in Southern California with a summit a significant distance above the tree line. As such its bright white winter snow cap, unobstructed by vegetation, makes the mountain noticeable from many miles away; the mountain hosts the longest recorded line of sight in the contiguous United States. San Gorgonio Mountain lies at the easternmost extremity of the Transverse Ranges; the mountain is a eroded dissected plateau. Big Bear Lake, California is the largest city near San Gorgonio, hosts two major ski resorts, as well as a popular summer get away for many southern Californians that utilize the lake for boating swimming, fishing; the shape of the mountain is influenced by a series of steeply dipping thrust faults on the north face of the mountain. The south side of the mountain contains river canyons typical of a dissected plateau; the mountain is a massive block of quartz monzonite, which sits on an ancient platform of Precambrian gneissic rocks.
Glacial and fluvial deposits dominate the surface of the lowest part of the mountain. Three major Southern California rivers have their source on San Gorgonio Mountain: the Santa Ana River, the Whitewater River, the San Gorgonio River. Jenks Lake, on the north slope of the mountain, is one of the few perennial lakes in Southern California. San Gorgonio Mountain sits on the Great Basin Divide, which separates steams that flow into the basins of the Basin and Range Province from rivers that flow into the Pacific Ocean; the climate on most of the mountain is Csb under the Köppen climate classification. The summit of San Gorgonio has an Alpine climate, as no month in that area has an average temperature greater than 10 °C. Like most other peaks in the Transverse Ranges, the summit is a technically easy class 1 hike. Several trails lead to the broad summit of San Gorgonio Mountain, which rises a few hundred feet above the tree line. Most routes are strenuous and require well over 4,000 feet of elevation gain.
The trail leading from the Fish Creek Trailhead to San Gorgonio Mountain has about 3,400 feet of gain, less than the routes from the South Fork and Vivian Creek trailheads. Hikers should always take caution. On December 1, 1952, a Douglas C-47, serial number 45-1124, crashed at the 11,000 feet level on the eastern face of the mountain; the C-47 was en route from Offutt Air Force Base, Nebraska to March Air Force Base near Riverside, California when it struck the mountain at night in the middle of a storm. "The aircraft was last heard from at 9:51 p.m. Pacific Standard Time, Monday." Thirteen people died. Nearly one month after the C-47 accident a Marine Corps HRS-2 helicopter, bureau number 129037, crashed on the mountain in coordination of the efforts of recovering the victims; the three crewmen of the helicopter survived the impact. Most of the wreckage of the two aircraft remain on the mountain and are accessible via the Fish Creek Trailhead or the South Fork Trailhead. In more recent years, the mountain claimed the lives of Frank Sinatra's mother and Dean Paul Martin, son of Dean Martin, in unrelated plane crashes.
Martin was an Air National Guard pilot and the McDonnell Douglas F-4C he was flying disappeared in a snowstorm and the wreckage was found on the mountain several days later. List of highest points in California by county List of Ultras of the United States "San Gorgonio". SummitPost.org. Retrieved 2011-05-07. "San Gorgonio Wilderness Association". Retrieved 2008-11-24. OnTheTrail.org - San Gorgonio Topo and Trail Map
Geographic coordinate system
A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position. A common choice of coordinates is latitude and elevation. To specify a location on a plane requires a map projection; the invention of a geographic coordinate system is credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC. A century Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning. In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, measured north or south of the island of Rhodes off Asia Minor.
Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. Ptolemy's 2nd-century Geography used the same prime meridian but measured latitude from the Equator instead. After their work was translated into Arabic in the 9th century, Al-Khwārizmī's Book of the Description of the Earth corrected Marinus' and Ptolemy's errors regarding the length of the Mediterranean Sea, causing medieval Arabic cartography to use a prime meridian around 10° east of Ptolemy's line. Mathematical cartography resumed in Europe following Maximus Planudes' recovery of Ptolemy's text a little before 1300. In 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, England as the zero-reference line; the Dominican Republic voted against the motion, while Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911.
In order to be unambiguous about the direction of "vertical" and the "horizontal" surface above which they are measuring, map-makers choose a reference ellipsoid with a given origin and orientation that best fits their need for the area they are mapping. They choose the most appropriate mapping of the spherical coordinate system onto that ellipsoid, called a terrestrial reference system or geodetic datum. Datums may be global, meaning that they represent the whole Earth, or they may be local, meaning that they represent an ellipsoid best-fit to only a portion of the Earth. Points on the Earth's surface move relative to each other due to continental plate motion and diurnal Earth tidal movement caused by the Moon and the Sun; this daily movement can be as much as a metre. Continental movement can be up to 10 m in a century. A weather system high-pressure area can cause a sinking of 5 mm. Scandinavia is rising by 1 cm a year as a result of the melting of the ice sheets of the last ice age, but neighbouring Scotland is rising by only 0.2 cm.
These changes are insignificant if a local datum is used, but are statistically significant if a global datum is used. Examples of global datums include World Geodetic System, the default datum used for the Global Positioning System, the International Terrestrial Reference Frame, used for estimating continental drift and crustal deformation; the distance to Earth's center can be used both for deep positions and for positions in space. Local datums chosen by a national cartographical organisation include the North American Datum, the European ED50, the British OSGB36. Given a location, the datum provides the latitude ϕ and longitude λ. In the United Kingdom there are three common latitude and height systems in use. WGS 84 differs at Greenwich from the one used on published maps OSGB36 by 112 m; the military system ED50, used by NATO, differs from about 120 m to 180 m. The latitude and longitude on a map made against a local datum may not be the same as one obtained from a GPS receiver. Coordinates from the mapping system can sometimes be changed into another datum using a simple translation.
For example, to convert from ETRF89 to the Irish Grid add 49 metres to the east, subtract 23.4 metres from the north. More one datum is changed into any other datum using a process called Helmert transformations; this involves converting the spherical coordinates into Cartesian coordinates and applying a seven parameter transformation, converting back. In popular GIS software, data projected in latitude/longitude is represented as a Geographic Coordinate System. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by'GCS North American 1983'; the "latitude" of a point on Earth's surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the Equator and to each other; the North Pole is 90° N. The 0° parallel of latitude is designated the Equator, the fun
The Coachella Valley is a desert valley in Southern California which extends for 45 mi in Riverside County southeast from the San Bernardino Mountains to the northern shore of the Salton Sea. It is the northernmost extent of the vast trough which includes the Salton Sea, the Imperial Valley and the Gulf of California, it is 15 mi wide along most of its length, bounded on the west by the San Jacinto Mountains and the Santa Rosa Mountains and on the north and east by the Little San Bernardino Mountains. The San Andreas Fault crosses the valley from the Chocolate Mountains in the southeast corner and along the centerline of the Little San Bernardinos; the fault is visible along its northern length as a strip of greenery against an otherwise bare mountain. The Chocolate Mountains are home to a United States Navy live gunnery range and are off-limits to the public; the Coachella Valley is sometimes referred to as the "Desert Empire" to differentiate it from the neighboring urbanized Inland Empire and the Imperial Valley.
Geographers and geologists sometimes call the area, along with the Imperial Valley to the south, the "Cahuilla Basin" or the "Salton Trough". The valley contains the resort cities of Palm Springs and Palm Desert, Rancho Mirage, Indio, La Quinta, Indian Wells and Cathedral City as well, altogether with a population of 500,000 in April, declining to around 200,000 in July and rising to around 800,000 by January, it is sometimes included in the Inland Empire region. Separate from the Inland Empire, it is a small to medium-sized metropolitan area consisting of Palm Springs and other smaller incoporated cities, consolidated into the Coachella Valley. Coachella Valley connects with the core of the Greater Los Angeles area to the west via the San Gorgonio Pass, a major transportation corridor that includes Interstate 10 and the Union Pacific Railroad. There is a large population of seasonal residents in the winter months, known as snowbirds, which at peak times may surpass 100,000 with another 3.5 million annual conventioneers and tourists.
There is some contention as to the origin of the name. Early maps show the area as "Conchilla," the Spanish word for "seashell." Since the area was once a part of a vast inland sea, tiny fossilized mollusk shells can be found in just about every remote area. Local lore explains the change in the name from Conchilla to Coachella as a mistake made by the map-makers contracted to transcribe the data supplied by the Southern Pacific Railroad's survey party. Rather than redraw the expensive maps, the railroad chose to instead begin calling the area by the misspelled name "Coachella" rather than its traditional name "Conchilla." Some believe that the name Coachella was made up, but that theory is rather unlikely. Though the area had been surveyed by Edward Fitzgerald Beale in 1857, whose survey party used camels to cross the desert along the path of the historic Bradshaw Trail, it wasn't until the coming of the Southern Pacific Railroad and the discovery of abundant artesian wells in the 19th Century that the area began to expand.
Cindarella Courtney was the first non-Indian child born in Indio in 1898. The first boy, David Elgin, was born in 1899; the coming in 1926 of U. S. Route 99 northward through Coachella and Indio and westward toward Los Angeles more or less along the present route of Interstate 10 helped further open both agriculture and tourism to the rest of the country. So too did the coming of State Highway 111 in the early 1930s, which cut a diagonal swath through the valley and connected all of its major settlements. Dr. June McCarroll a nurse with the Southern Pacific whose office fronted U. S. 99 in Indio, is credited with being the first person to delineate a divided highway by painting a stripe down the middle of the roadbed in response to frequent head-on collisions. The standard was adopted worldwide. Doctor McCarroll is memorialized by a stretch of I-10 through Indio named in her honor; the Coachella Valley was popular among celebrities from Frank Sinatra to Dakota Fanning who came and continue to come to enjoy vacations and winter homes in the desert resort community.
It became a major real estate destination in the 1980s and 1990s, no longer limited to senior citizens, winter residents and retirees. Families with young children and young adults became interested in Palm Springs and surrounding communities for lower cost housing and apartment rents. Palm Springs has become a world-famous tourist attraction; as a tourist destination, the Coachella Valley can be considered a Southwest attraction like Las Vegas, Phoenix, or Santa Fe, or as a part of Southern California along with San Diego, Orange County, Los Angeles. In a 2003 Condé Nast publication review, Palm Springs was ranked one of the top 10 global vacation destinations, the smallest one in population; the area is surrounded on the southwest by the Santa Rosa Mountains, by the San Jacinto Mountains to the west, the Little San Bernardino Mountains to the east and San Gorgonio Mountain to the north. These tend to average between 5,000 and 7,000 feet. Elevations on the Valley floor range from 1,600 feet above sea level at the north end of the Valley to 250 feet below sea level around Mecca.
In the summer months daytime temperatures range from 104 °F to 112 °F and nighttime lows from 75 °F to 86 °F. During winter, the daytime temperatures range from 68 °F to 88 °F and corresponding nights range from 46 °F to 65 °F making it a popular winter resort destination; the surrounding mountains create T
San Andreas Fault
The San Andreas Fault is a continental transform fault that extends 1,200 kilometers through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, its motion is right-lateral strike-slip; the fault divides into three segments, each with different characteristics and a different degree of earthquake risk. The slip rate along the fault ranges from 20 to 35 mm /yr; the fault was identified in 1895 by Professor Andrew Lawson of UC Berkeley, who discovered the northern zone. It is described as having been named after San Andreas Lake, a small body of water, formed in a valley between the two plates. However, according to some of his reports from 1895 and 1908, Lawson named it after the surrounding San Andreas Valley. Following the 1906 San Francisco earthquake, Lawson concluded that the fault extended all the way into southern California. In 1953, geologist Thomas Dibblee concluded that hundreds of miles of lateral movement could occur along the fault. A project called the San Andreas Fault Observatory at Depth near Parkfield, Monterey County, was drilled through the fault during 2004 – 2007 to collect material and make physical and chemical observations to better understand fault behavior.
The northern segment of the fault runs from Hollister, through the Santa Cruz Mountains, epicenter of the 1989 Loma Prieta earthquake up the San Francisco Peninsula, where it was first identified by Professor Lawson in 1895 offshore at Daly City near Mussel Rock. This is the approximate location of the epicenter of the 1906 San Francisco earthquake; the fault returns onshore at Bolinas Lagoon just north of Stinson Beach in Marin County. It returns underwater through the linear trough of Tomales Bay which separates the Point Reyes Peninsula from the mainland, runs just east of Bodega Head through Bodega Bay and back underwater, returning onshore at Fort Ross. From Fort Ross, the northern segment continues overland, forming in part a linear valley through which the Gualala River flows, it goes back offshore at Point Arena. After that, it runs underwater along the coast until it nears Cape Mendocino, where it begins to bend to the west, terminating at the Mendocino Triple Junction; the central segment of the San Andreas Fault runs in a northwestern direction from Parkfield to Hollister.
While the southern section of the fault and the parts through Parkfield experience earthquakes, the rest of the central section of the fault exhibits a phenomenon called aseismic creep, where the fault slips continuously without causing earthquakes. The southern segment begins near California. Box Canyon, near the Salton Sea, contains upturned strata associated with that section of the fault; the fault runs along the southern base of the San Bernardino Mountains, crosses through the Cajon Pass and continues northwest along the northern base of the San Gabriel Mountains. These mountains are a result of movement along the San Andreas Fault and are called the Transverse Range. In Palmdale, a portion of the fault is examined at a roadcut for the Antelope Valley Freeway; the fault continues northwest alongside the Elizabeth Lake Road to the town of Elizabeth Lake. As it passes the towns of Gorman, Tejon Pass and Frazier Park, the fault begins to bend northward, forming the "Big Bend"; this restraining bend is thought to be where the fault locks up in Southern California, with an earthquake-recurrence interval of 140–160 years.
Northwest of Frazier Park, the fault runs through the Carrizo Plain, a long, treeless plain where much of the fault is plainly visible. The Elkhorn Scarp defines the fault trace along much of its length within the plain; the southern segment, which stretches from Parkfield in Monterey County all the way to the Salton Sea, is capable of an 8.1-magnitude earthquake. At its closest, this fault passes about 35 miles to the northeast of Los Angeles; such a large earthquake on this southern segment would kill thousands of people in Los Angeles, San Bernardino and surrounding areas, cause hundreds of billions of dollars in damage. The Pacific Plate, to the west of the fault, is moving in a northwest direction while the North American Plate to the east is moving toward the southwest, but southeast under the influence of plate tectonics; the rate of slippage averages about 33 to 37 millimeters a year across California. The southwestward motion of the North American Plate towards the Pacific is creating compressional forces along the eastern side of the fault.
The effect is expressed as the Coast Ranges. The northwest movement of the Pacific Plate is creating significant compressional forces which are pronounced where the North American Plate has forced the San Andreas to jog westward; this has led to the formation of the Transverse Ranges in Southern California, to a lesser but still significant extent, the Santa Cruz Mountains. Studies of the relative motions of the Pacific and North American plates have shown that only about 75 percent of the motion can be accounted for in the movements of the San Andreas and its various branch faults; the rest of the motion has been found in an area east of the Sierra Nevada mountains called the Walker Lane or Eastern California Shear Zone. The reason for this is not clear. Several hypotheses have been offered and research is ongoing. One hypothesis – which gained interest following the Landers earthquake in 1992 – suggests the plate boundary may be shifting eastward aw