128-566: The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the U.S. state of California . It forms part of the tectonic boundary between the Pacific plate and the North American plate . Traditionally, for scientific purposes, the fault has been classified into three main segments (northern, central, and southern), each with different characteristics and
256-482: A Manila galleon laden with a luxury cargo of Chinese silks, spices, and Ming porcelain bound for Acapulco, Cermeno endured both the first of hundreds of documented shipwrecks at Point Reyes, as well as one of the most amazing journeys to safety. Among the crew were Filipino mariners. Struggling with a decrepit, heavily laden ship and a tired crew, Cermeno explored the California coast, eventually anchoring near
384-500: 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 movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults
512-617: A spreading center between the Pacific plate and the Farallon plate (which is now mostly subducted, with remnants including the Juan de Fuca plate , Rivera plate , Cocos plate , and the Nazca plate ) was beginning to reach the subduction zone off the western coast of North America. As the relative motion between the Pacific and North American plates was different from the relative motion between
640-499: A 1956 National Park Service (NPS) study of possible seashore parks recommended acquisition of the peninsula. By 1958, a report was published recommending immediate NPS acquisition of 35,000 acres. Controversy raged, with environmentalists applauding the proposal and the ranchers opposing it. A compromise was crafted which allowed the ranchers to lease their land and continue dairying while coexisting with tourists and park activities. On September 13, 1962, President John F. Kennedy signed
768-655: A 1977 study. Tule elk became infected within two years of their reintroduction to the peninsula with this disease, which was brought to North America with Eurasian cattle . Another nonnative, bacterial disease, brucellosis , can induce abortions in pregnant cattle, elk, and bison, and was also brought to North America by importation of Eurasian cattle. Pt. Reyes cattle have also infected the tule elk population. Non-native axis deer and fallow deer (originally from India and Asia Minor , respectively) used to inhabit Point Reyes, where they competed with native black-tailed deer ( Odocoileus hemionus columbianus ). A doctor bought
896-485: A Mexican citizen and colonel in the army. This land grant was also in the Olema Valley , and, to add to the boundary confusion, he soon left the area and hired Garcia to oversee it. A mere two years later, Berry sold nearly 9,000 acres (3,642 ha) of it to a sea captain, Joseph Snook, an act clearly prohibited by Mexican law and grounds for forfeiture of the entire grant. Although Berry understandably wanted to keep
1024-483: A centrally located town for supplies, services, and entertainment. In 1857, a hotel and saloon were built and the young town was named "Olema", meaning "coyote" in the Coast Miwok dialect. Within three years, it had emerged as the region's commercial center with a post office, grocery store, saloon, butcher, livery stable, and two hotels. By 1867, a wagon road from San Rafael was built and a stage coach arrived twice
1152-704: A confusing series of sales and transfers that no one seemed to be able to untangle. Finally, in 1844, the rancheros themselves asked the Mexican government to investigate titles and clarify ownership. Little was clarified, and it was not until the United States took possession of California and required rancheros to conduct surveys and make court appearances to retain their land that the confusing pattern of sales and trades were untangled. Most rancheros were eventually able to prove ownership. Unfortunately, by this time, they had run out of cash and were forced to sell to pay
1280-589: A different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm (0.79 to 1.38 in) per year. In the north, the fault terminates offshore near Eureka, California , at the Mendocino triple junction , where three tectonic plates meet. The Cascadia subduction zone intersects the San Andreas fault at the Mendocino triple junction. It has been hypothesized that
1408-405: A fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between
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#17327574535541536-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving
1664-489: A fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas
1792-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
1920-427: A hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through the stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in
2048-536: A lawyer, to join him. They became known as San Francisco's foremost authorities on title litigation. Using their title expertise, they began acquiring Point Reyes land. When Oscar's oldest daughter married Charles Webb Howard , also a lawyer, the trio partnered to transform windswept Point Reyes into prosperous dairies. Determined to supply booming San Francisco with its butter, by 1857, the partners began fencing significant expanses of land (eventually resulting in 40 miles of fencing), building homes and barns, and stocking
2176-560: A link between the water level in Lake Cahuilla (now the Salton Sea ) and seismic activity along the southern San Andreas Fault. The study suggests that major earthquakes along this section of the fault coincided with high water levels in the lake. The hydrological load caused by high water levels can more than double the stress on the southern San Andreas Fault, which is likely sufficient for triggering earthquakes. This may explain
2304-558: A lovely land populated by friendly tribes, Spain neglected California until the second half of the 18th century. By that time, trade had become an important source of income, and it was becoming clear that the nation controlling California's harbors would reap incredible profits. When England, France, and Russia began to covet California's coast, the King of Spain knew it was time to fortify it. The Portolá expedition of 67 men and 100 pack mules left San Diego in 1769. Led by Gaspar de Portolá ,
2432-562: A magnitude 7.8 earthquake along the southern San Andreas Fault could cause about 1,800 deaths and $ 213 billion in damage. This scenario hypothesizes the potential effects of a 7.0 magnitude earthquake on the San Andreas Fault in the San Francisco Bay Area. It aims to estimate the impacts on urban infrastructures along with the rebuilding efforts to both the landscape and economy. This study combines not only
2560-534: A major earthquake along the Cascadia subduction zone could trigger a rupture along the San Andreas Fault. In the south, the fault terminates near Bombay Beach, California , in the Salton Sea . Here, the plate motion is being reorganized from right-lateral to divergent . In this region (known as the Salton Trough ), the plate boundary has been rifting and pulling apart, creating a new mid-ocean ridge that
2688-484: A major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by
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#17327574535542816-400: A manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along a decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of
2944-473: A master plan calling for a population of 28,000 by imposing a moratorium on new homes and defeating efforts to widen its access highway. Instead, a plan was approved that made agriculture, fishing, and small business the town's economic base. Bolinas soon gained renown for its unusual structures and recreational drug use. As soon as the Shafter dairies began to thrive, it became evident that Point Reyes needed
3072-421: A non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In
3200-715: A portion of the fault is easily 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 roughly 140–160 years. Northwest of Frazier Park,
3328-547: A remnant population of eight individuals was discovered on Guadalupe Island in 1892 by a Smithsonian expedition, who promptly killed seven of the eight for their collections. The elephant seals managed to survive, and were finally protected by the Mexican government in 1922. Subsequently, the U.S. protection was strengthened after passage of the Marine Mammal Protection Act in 1972, and numbers have now recovered to over 100,000. The first breeding pair
3456-464: A reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of the fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on
3584-658: A single herd on Pt. Reyes in the 1840's. Stephen J. Richardson, son of Marin County pioneer Captain William A. Richardson , wrote "I think the largest herd in the world roamed over the deep grasslands of Point Reyes...I fully believe there were a thousand elk in one herd." Although they had been completely extirpated from Point Reyes, in 1978, ten elk were reintroduced to Point Reyes from the San Luis National Wildlife Refuge near Los Banos . By 2009,
3712-645: A staple, as they could be stored in dry granaries to provide sustenance when food was less plentiful. Although the Coast Miwok periodically interacted with European explorers, they continued their habitation until late in the 18th century when the Spanish built Mission San Rafael and missionaries began journeying to Point Reyes to recruit them to move to the mission. While attempting to convert them, these missionaries introduced diseases that brought many deaths, fewer births, and significantly increasing infant mortality rates. In 1992, Coast Miwok descendants established
3840-519: A week. Druids Hall was completed in 1885. While this Olema chapter of the United Ancient Order of Druids adhered to principles of mutual support, intellectual growth, and social consciousness, it also served as a temperance society. The Shafters lobbied hard for a railroad to serve Point Reyes. When it was finally built, it bypassed Olema, terminating, instead, two miles away. When the first train arrived early in 1875, Point Reyes Station
3968-422: Is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near the surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in
San Andreas Fault - Misplaced Pages Continue
4096-499: Is a combined effort from experts in the physical sciences, social sciences, and engineering both in the public and private sectors- ranging from urban planners to economists/business professionals. Not only does this study aim to estimate the impacts of the event, but aims to estimate the years of rebuilding and funding needed to recover communities from a potential disaster such as the HayWired Scenario. The first volume of
4224-423: Is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of the fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of
4352-607: Is an extension of the Gulf of California . Sediment deposited by the Colorado River is preventing the trough from being filled in with sea water from the gulf. The fault was first identified in 1895 by Professor Andrew Lawson of UC Berkeley . In the wake of the 1906 San Francisco earthquake , Lawson was tasked with deciphering the origin of the earthquake. He began by surveying and mapping offsets (such as fences or roads that had been sliced in half) along surface ruptures. When
4480-478: Is approximately 30 miles (50 km) west-northwest of San Francisco . The term is often applied to the Point Reyes Peninsula , the region bounded by Tomales Bay on the northeast and Bolinas Lagoon on the southeast. The majority of the peninsula as well as the headlands are protected as part of Point Reyes National Seashore . The cape protects Drakes Bay on its southern side. The headland
4608-544: Is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms a plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or
4736-611: Is largely drained by Drakes Estero . Drakes Bay and Drake's Estero are named after English seafarer Sir Francis Drake who possibly hauled his ship, the Golden Hinde , up onto the beach for repairs in June 1579. Inverness Ridge runs along the peninsula's northwest-southeast spine, with forested peaks around 430 metres (1,410 ft). West of the ridge, the land flattens out and the vegetation turns to scrub . The Mount Vision fire in 1995 burned part of Inverness Ridge, as well as
4864-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of
4992-492: Is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering , a fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing
5120-700: Is structurally dominated by the Point Reyes Syncline . The Point Reyes Peninsula is on the Pacific Plate , while the rest of Marin County land is on the North American Plate . The peninsula is a member of the Salinian Block , a segment of the southernmost Sierra Nevada range transported north from Southern California by movement along the San Andreas fault. Simply speaking, the peninsula consists of three major members:
5248-410: Is that Lawson named the fault after this lake. However, according to some of his reports from 1895 and 1908, he actually named it after the surrounding San Andreas Valley. Following the 1906 San Francisco earthquake, Lawson also 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
San Andreas Fault - Misplaced Pages Continue
5376-425: Is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However,
5504-419: The 1994 Northridge earthquake ) occurs about once every 6.7 years statewide. The same report also estimated there is a 7% probability that an earthquake of magnitude 8.0 or greater will occur in the next 30 years somewhere along the San Andreas Fault. A different USGS study in 2008 tried to assess the physical, social and economic consequences of a major earthquake in southern California. That study predicted that
5632-762: The Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are the most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to
5760-702: The Coast Miwok to the mission. Although they were successful in convincing many to settle at the mission, it was soon clear that the Coast Miwoks were not thriving. Serious outbreaks of smallpox and pneumonia killed many. Those who survived sickened from a wide variety of other illnesses, such as colds and measles. Birth rates dropped, and mortality rates increased at an alarming rate. Since the missions depended upon healthy workers for their prosperity, these illnesses foretold their demise. In 1821, Mexico gained independence from Spain and possession of California in
5888-524: The Farallon Islands . The expedition was blocked from going farther north toward Point Reyes by the Golden Gate and San Francisco Bay, since they had no boats. Beginning with Portolá's expedition, Spain began establishing presidios and Spanish missions in California ((1769–1833)). By 1817, Mission San Rafael was established and padres began journeying to Point Reyes, intent on enticing
6016-492: The Mexican War of Independence . Most mission land was subdivided and into large land grants used mainly for cattle ranching. In 1843, Point Reyes itself and Drake's Bay being mostly unsuitable for cattle, became part of Rancho Punta de los Reyes Sobrante ( Sobrante means "leftover"). This was only a few years before cession of California to the United States, which led to decades of confusion and boundary battles. When
6144-618: The Salton Sea , contains upturned strata associated with that section of the fault. The fault then runs along the southern base of the San Bernardino Mountains , crosses through 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 commonly called the Transverse Range. In Palmdale ,
6272-560: The San Andreas Fault . Its core is granite, unlike the terrain east of Tomales Bay. The granite rocks that form the peninsula were once continuous with the Tehachapi Mountains , which is located 350 mi (563 km) south of here. In the 1906 earthquake , Point Reyes moved north 21 ft (6.4 m). Point Reyes is bounded to the east by the San Andreas Fault , which runs directly under Tomales Bay, and
6400-645: The Santa Cruz Mountains , epicenter of the 1989 Loma Prieta earthquake , then up the San Francisco Peninsula , where it was first identified by Professor Lawson in 1895, then 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
6528-644: The Spanish missions in California were dismantled, virtually all of Point Reyes was given to 'Rafael Garcia, a corporal in the Mexican Army, who was awarded two leagues (8,911 acres (3,606 ha)) in March 1836. Named Rancho Tomales y Baulines , it is believed to have included the entire Olema Valley from Tomales Bay to Bolinas Lagoon, although its borders were never clearly defined. Garcia's failure to survey and confirm boundaries, as required by Mexican law, set
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#17327574535546656-525: The U.S. Geological Survey (USGS) have made variable predictions as to the risk of future seismic events. The ability to predict major earthquakes with sufficient precision to warrant increased precautions has remained elusive. The U.S. Geological Survey's most recent forecast, known as UCERF3 (Uniform California Earthquake Rupture Forecast 3), released in November 2013, estimated that an earthquake of magnitude 6.7 M or greater (i.e. equal to or greater than
6784-519: The Woodward fire in 2020. Point Reyes lends its name to the town of Point Reyes Station . The point may once have been known as Lobes Lighthouse by the sailors of clipper ships on the meat trade. (Lobes are ridges of slide material commonly referred to in the literature from erosion events and the point is of that shape out to sea.) The contemporary inhabitants of the Point Reyes area at
6912-548: The eastern California shear zone . This complicated evolution, especially along the southern segment, is mostly caused by either the "Big Bend" and/or a difference in the motion vector between the plates and the trend of the fault and its surrounding branches. The fault was first identified in Northern California by UC Berkeley geology professor Andrew Lawson in 1895 and named by him after the surrounding San Andreas valley. Eleven years later, Lawson discovered that
7040-657: The seismic shaking and tsunami hazard to infrastructure and people in the vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
7168-571: The 31 dairies they established still operate today. Oscar was the first to arrive. A Vermont lawyer intent upon making his fortune and returning home as soon as possible, he left his family to journey to booming San Francisco. His separation from them became intolerable when his two youngest children died while he was away. Still not willing to give up the promise of wealth, he convinced his wife to come, bringing their surviving daughter. They thrived, and Oscar fathered four more California-born daughters. Oscar soon convinced his younger brother, James, also
7296-527: The 70 surviving crew members to begin the long journey home. After a grueling two-month voyage, remembered as a remarkable feat of seamanship, Cermeno and all crew arrived safely in Acapulco in January 1596. Despite his amazing journey, Cermeno received no celebratory welcome, for he had not only lost his ship and cargo, but had also failed to locate the safe harbor he was ordered to find. Despite reports of
7424-586: The California economy within the first 6 months post-recovery from the event through estimates of "utility outages, property damages, and supply chain disruptions resulting in an estimated $ 44 billion of gross state product (GSP) losses, or translated at 4% of the California economy"(Wein et al.). This study also projects the recovery of jobs lost in highly impacted areas, such as Alameda County, could take up to 10 years to fully recover job losses and possible economic recession. Trajectories for economic recovery are improved by reconstruction but also delayed with impacts to
7552-687: The Farallon and North American plates, the spreading ridge began to be "subducted", creating a new relative motion and a new style of deformation along the plate boundaries. These geological features are what are chiefly seen along San Andreas Fault. It also includes a possible driver for the deformation of the Basin and Range , separation of the Baja California peninsula , and rotation of the Transverse Range . The main southern section of
7680-776: The Federated Indians of Graton Rancheria, and in December 2000, legislation passed granting the tribe federal recognition. The tribe has almost 500 members, who engage in a revival of traditional customs and ceremonies, often held in Kule Loklo , "Valley of the Bear", a replica Miwok village in Point Reyes National Seashore . On November 13, 1542, Spanish explorer Juan Rodríguez Cabrillo sighted and named "Cabo de Pinos" (Point Reyes), but missed
7808-475: The Garcias continued ranching, their land began to disappear until, after 15 years of litigation, multiple court appearances, and high legal fees, Garcia had sold all but 3,085 acres (1,248 ha) of his grant at bargain prices. Although Garcia believed he owned virtually all of Point Reyes, another Point Reyes land grant was awarded the same year, 1836. It was given to an Irishman, James Berry, who had become
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#17327574535547936-659: The HayWired Scenario study was released in 2017, with consistent continuations and contributions by engineers. This continuation was published in the second volume, Engineering Implications, in 2018. As of the 2021 Fact sheet update, there are several estimates on damages ranging from the approximate people affected at home, work, effects of lifeline infrastructures such as telecommunications, and more. This group of scientists have worked together to create estimates of how hazards such as liquefaction, landslides, and fire ignition will impact access to utilities, transportation, and general emergency services. This study goes into detail about
8064-689: 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, and to a lesser but still significant extent, the Santa Cruz Mountains (the location of the Loma Prieta earthquake in 1989). 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
8192-540: The Philippines and Acapulco passed by Point Reyes, some even anchoring briefly, it is the landing by Sir Francis Drake that dominates discussion of this era of Point Reyes early history. On June 17, 1579, during his circumnavigation , he landed in the vicinity of Point Reyes and proclaimed it Nova Albion ('New Britain') . The National Historic Landmark designation has the landing as Drake's Cove at Point Reyes National Seashore. Drake's chaplain's observations about
8320-413: The Point Reyes inlet now called Drakes Estero. Within a few days, a November storm beached the ship where it listed and was relentlessly pounded by the furious surf. It soon broke apart, killing several men and dumping the precious cargo, some of which was eventually collected and used by the local Coast Miwok inhabitants. Cermeno salvaged a small, open launch, likened to a large canoe, and loaded it with
8448-761: The Salinian Cretaceous crystalline basement, the overlying Pliocene sedimentary rocks, and the late Pleistocene marine terrace deposits of the southern peninsula. The U.S. Weather Bureau (now the National Weather Service ) maintained a cooperative weather station in the Point Reyes lighthouse from 1914 to 1943, though temperatures were only tracked through 1926. Based on those records, average January temperatures ranged from 45.1 to 54.1 °F (7.3 to 12.3 °C) and average September temperatures ranged from 51.7 to 61.0 °F (10.9 to 16.1 °C). The highest temperature recorded
8576-466: The San Andreas Fault near Parkfield in central California consistently produces a magnitude 6.0 earthquake approximately once every 22 years. Following recorded seismic events in 1857, 1881, 1901, 1922, 1934, and 1966, scientists predicted that another earthquake should occur in Parkfield in 1993. It eventually occurred in 2004 . Due to the frequency of predictable activity, Parkfield has become one of
8704-474: The San Andreas Fault proper has only existed for about 5 million years. The first known incarnation of the southern part of the fault was Clemens Well-Fenner- San Francisquito fault zone around 22–13 Ma. This system added the San Gabriel Fault as a primary focus of movement between 10–5 Ma. Currently, it is believed that the modern San Andreas will eventually transfer its motion toward a fault within
8832-421: The San Andreas Fault stretched southward into southern California after reviewing the effects of the 1906 San Francisco earthquake . Large-scale (hundreds of miles) lateral movement along the fault was first proposed in a 1953 paper by geologists Mason Hill and Thomas Dibblee . This idea, which was considered radical at the time, has since been vindicated by modern plate tectonics . Seismologists discovered that
8960-462: The San Andreas fault has reached a sufficient stress level for an earthquake of magnitude greater than 7.0 on the moment magnitude scale to occur. This study also found that the risk of a large earthquake may be increasing more rapidly than scientists had previously believed. Moreover, the risk is currently concentrated on the southern section of the fault, i.e. the region around Los Angeles, because strong earthquakes have occurred relatively recently on
9088-513: The San Andreas towards Walker Lane. Assuming the plate boundary does not change as hypothesized, projected motion indicates that the landmass west of the San Andreas Fault, including Los Angeles, will eventually slide past San Francisco, then continue northwestward toward the Aleutian Trench , over a period of perhaps twenty million years. The San Andreas began to form in the mid- Cenozoic about 30 Mya (million years ago). At this time,
9216-403: The Spanish. Their trade between the Philippines and Mexico was booming, and they were constantly seeking safe harbors along their route. Many believe that Drake's discovery of such a harbor inspired the Spanish to order Sebastian Rodriguez Cermeno , a Portuguese captain trading for Spain, to survey the California coast on his journey to Mexico from the Philippines in 1595. Commanding San Agustin ,
9344-522: The United States, Garcia continued to prosper. Soon after the American takeover, the 1849 California gold rush brought floods of prospectors. Where his wild cattle had been valued only for hides and tallow, he could now sell them to feed hungry gold-seekers, netting as much as $ 35 each. Unfortunately for Garcia, these gold-rich years ended quickly: in 1851, the United States passed a law requiring rancheros to prove legal ownership of their land grants. While
9472-575: The abnormally long period of time since the last major earthquake in the region since the lake has dried up. The San Andreas Fault System has been the subject of a flood of studies. In particular, scientific research performed during the last 23 years has given rise to about 3,400 publications. A study published in 2006 in the journal Nature by Yuri Fialko, an associate professor at the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps Institution of Oceanography , found that
9600-404: The areas inhabitants suggest the landing occurred near a Coast Miwok settlement. These notes describe the genial welcome Drake and his men received, complete with ceremony and gifts, as well as the landscape and wildlife, and included commentary about fog which frequently obscures the peninsula during the summer months. Rumors of Drake's discovery of a safe harbor on the California coast intrigued
9728-625: The axis and fallow deer from the San Francisco Zoo in 1948 for his 5,000-acre hunting club, which later became part of the national seashore. In 2006, the park embarked on a plan to eradicate the non-native deer via contraception and culling, which succeeded despite controversy, over a twenty year program. Vegetation native to Point Reyes includes bishop pine , Douglas-fir , coyote brush , monkeyflower , poison oak , California blackberry , salal and coast redwood , among others. Nearly 490 different species of birds have been observed in
9856-449: The bill authorizing the acquisition of 53,000 acres and allocating $ 13 million. Eventually 18,000 acres purchased by the NPS were leased back to ranchers. In cooperation with the NPS, volunteers have restored and maintain a historic coastal radiotelegraph marine station, KSM (ex- KPH ), at Point Reyes. It remains one of the few commercial Morse code stations operating in the world, and is
9984-403: The brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when the strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of
10112-1194: The central ( 1857 ) and northern ( 1906 ) segments of the fault, while the southern section has not seen any similar rupture for at least 300 years. According to this study, a major earthquake on that southern section of the San Andreas fault would result in major damage to the Palm Springs – Indio metropolitan area and other cities in San Bernardino , Riverside and Imperial counties in California, and Mexicali Municipality in Baja California . It would be strongly felt (and potentially cause significant damage) throughout much of Southern California , including densely populated areas of Los Angeles County , Ventura County , Orange County , San Diego County , Ensenada Municipality and Tijuana Municipality , Baja California, San Luis Rio Colorado in Sonora and Yuma, Arizona . Older buildings would be especially prone to damage or collapse, as would buildings built on unconsolidated gravel or in coastal areas where water tables are high (and thus subject to soil liquefaction ). Of
10240-430: The characteristic high fog. When foggy, visibility is so slim that one cannot even view the lighthouse from the top of the approximately 300 steps necessary to walk down to reach it. The lighthouse serves a great purpose in such a foggy area, as there is no beach to wash up on; it is on a rocky cliff. Day or night, the light may be the only thing visible to ships. The peninsula is a popular recreational destination for
10368-467: The construction industry. A 2008 paper, studying past earthquakes along the Pacific coastal zone, found a correlation in time between seismic events on the northern San Andreas Fault and the southern part of the Cascadia subduction zone (which stretches from Vancouver Island to Northern California). Scientists believe quakes on the Cascadia subduction zone may have triggered most of the major quakes on
10496-426: The dairies with the pure-bred bulls and rams, some costing over $ 1,400. By 1868, they had 3,500 cows on 17 dairies and were producing over 700,000 pounds of butter a year. All their dairies were operated by renters. When the most industrious of these renters tried to buy the dairy they worked, they failed. Many eventually left, establishing some of California's other major dairies. Despite their boundless optimism about
10624-436: The direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and the footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each
10752-486: The elk there dying from lack of water. In 2012 there were 540 elk, then only 357 in 2013, and by 2014 only 286. In August and September 2020, drought and wildfires again threaten the Tomales Point elk, leading some conservationists to illegally bring water to the elk north of the fence. Half of the ten Point Reyes dairy cattle herds were infected with paratuberculosis (aka Johne's Disease) along with exotic deer in
10880-706: The entrance to San Francisco Bay , a lapse that mariners would repeat for the next two centuries and more, due to the fog that characterizes the area. The Spanish explorer Sebastián Vizcaíno named the land Punto de los Reyes ("Kings' Point") when his ship, the Capitana , anchored in Drakes Bay on the Day of the Three Kings ( Epiphany , or the end of the 12 Days of Christmas) on January 6, 1603. Although early explorers and Spanish trading galleons journeying between
11008-456: The fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and the implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect
11136-402: The fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of the fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding
11264-576: The fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with
11392-401: The fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into the geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in
11520-540: 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 (56 km) to
11648-427: The fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining
11776-493: The fault. A National Science Foundation funded project called the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, California , involved drilling through the fault from 2004 to 2007. The aim was to collect core samples and make direct geophysical and geochemical observations to better understand fault behavior at depth. The northern segment of the fault runs from Hollister , through
11904-475: The gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of
12032-432: The geological impacts/effects of the event, but also the societal impacts such as property damage, economic rebuilding, and aims at estimating damages if cities increased risk-reduction. It was developed for preparedness geared towards Bay Area residents and as a warning with an attempt to encourage local policy makers to create infrastructure and protections that would further risk reduction and resilience-building. This study
12160-460: The governor of Baja California, they began walking to the largest known harbor, Monterey Bay . Portolá expected more of a harbor than what they found at Monterey, and decided they must not have reached it yet. Pushing on north along the coast, they instead discovered San Francisco Bay . Prior to that, from a high point on the coast south of Pacifica , they saw and recognized (from the description of Manila Galleon pilot Cabrera Bueno) Point Reyes and
12288-418: The grazing of the elk is Holcus lanatus . By grazing the land, the elk promote native species to flourish. This action allows for the open grassland to be sustained and supports the overall ecosystem. The interaction is a cruel aspect that highlights the important of preserving the ecological balance at Point Reyes. The entire Point Reyes Peninsula is a piece of the Salinian Block transported northward by
12416-522: The influence of plate tectonics . The rate of slippage averages about 33 to 37 millimeters (1.3 to 1.5 in) 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 also creating significant compressional forces which are especially pronounced where
12544-475: 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 . (In this region around the San Francisco Bay Area several significant "sister faults" run more-or-less parallel, and each of these can create significantly destructive earthquakes.) From Fort Ross,
12672-537: The local post office, while the former engine house was converted into a community center. In the 1970s, hippies established cottage industries in abandoned houses and shops. At the same time, the Coast Guard bought 30 acres of land formerly used as cattle pens, and built military housing. Continuing as the region's supply and service center, it is a popular destination with shops, restaurants, and an annual music festival. As developers and loggers submitted plans,
12800-422: The location of these offsets were plotted on a map, he noted that they made a near perfect line on top of the fault he previously discovered. He concluded that the fault must have been the origin of the earthquake. This line ran through San Andreas Lake , a sag pond . The lake was created from an extensional step over in the fault, which created a natural depression where water could settle. A common misconception
12928-406: The most important areas in the world for large earthquake research. In 2004, work began just north of Parkfield on the San Andreas Fault Observatory at Depth (SAFOD). The goal of SAFOD is to drill a hole nearly 3 kilometres (1.9 mi) into the Earth's crust and into the San Andreas Fault. An array of sensors will be installed to record earthquakes that happen near this area. A 2023 study found
13056-627: 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 away from
13184-502: The nearby San Francisco Bay Area , especially for hiking on its many trails and sea kayaking the shores of Tomales Bay and the coast. There are close to 150 miles (241 km) of trails, including the popular Bear Valley Trail, which starts from the Visitor Center. Point Reyes National Seashore offers some of the finest birdwatching in the United States. It is also one of the best places to watch northern elephant seals in
13312-480: The northeast of Los Angeles. Such a large earthquake on this southern segment would kill thousands of people in Los Angeles, San Bernardino, Riverside, and surrounding areas, and 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 relatively southeast under
13440-519: The northern San Andreas within the past 3,000 years. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. However the 1906 San Francisco earthquake seems to have been the exception to this correlation because the plate movement was mostly from south to north and it was not preceded by a major quake in the Cascadia zone. The San Andreas Fault has had some notable earthquakes in historic times: Fault (geology)#Strike-slip faults In geology ,
13568-497: 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
13696-557: The only one in the U.S. During the Cold War , submarines repaired at Mare Island Naval Shipyard were tested in the shallow waters off Point Reyes following shipyard repairs. Navy safety personnel used a small monitoring and communications hut on the peninsula for monitoring submarines during these sea trials . In April and May 1979, part of John Carpenter 's The Fog was shot at the Point Reyes Lighthouse and
13824-500: The original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to the footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other,
13952-404: The park and on adjacent waters. Tule elk within this region primarily consume native grasses and forbs such as Nassella pulchra . This is an essential aspect that helps maintain the biodiversity of the grassland ecosystem. The interaction between these plants and the elk helps prevent the encroachment of invasive shrubs and non-native species. An example of a species that can be prevented through
14080-527: The population climbed to over 440 elk at Tomales Point 's 2,600 acres of coastal scrub and grasslands. In 1999, 100 elk from Tomales Point were moved to the Limantour wilderness area of the Seashore and above Drakes Beach to Ranch A, as that ranch's long-term lease expired and was not renewed. The drought in 2012–2015 was also a threat to the elk confined north of the fence on Tomales Point, with nearly half
14208-676: The population may have fallen as low as 20. In 1874 American whaleman Charles Melville Scammon recorded in Marine Mammals of the Northwestern Coast of America , that "the elephant seal...known to the Old Californians as Elefante marino had a geographical distribution from Cape Lazaro (about 1/4 of the way up the Baja peninsula) in the south to Point Reyes in the north". They were thought to be extinct in 1884 until
14336-581: The promise of Point Reyes, they were plagued by financial worries. After they passed, their children tried to hold on to the dairies, trying unsuccessfully to stop their decline despite aging ranches, sickening herds, and often unhappy tenants. Finally, in 1937, an era ended when the last of the Shafter Empire was sold, ushering in a new parade of owners. Four towns can be found on Point Reyes: Bolinas , Olema , Inverness , and Point Reyes Station . During Spanish and Mexican War, Bolinas' remote lagoon
14464-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
14592-467: The sale secret, Snook wanted legal title. He discovered that the only way he could obtain legal title of the land he had illegally purchased was to formally denounce Berry's ownership on the grounds that he had never occupied it. He was successful and gained legal title to the land he had illegally purchased, stocked it with 56 head of cattle, and, like Berry, hired Garcia to oversee it. Three months after he won legal title, he illegally sold it. And so began
14720-556: The size of the weathered zone and hence creates more space for groundwater . Fault zones act as aquifers and also assist groundwater transport. Point Reyes Peninsula Point Reyes ( / ˈ r eɪ . ɪ s / RAY -iss Spanish : Punta de los Reyes , meaning ' Cape of the Kings ') is a prominent landform and popular tourist destination on the Pacific coast of Marin County in Northern California . It
14848-446: The small town of Inverness . As of 2015, Drakes Bay Oyster Company (DBOC) has ceased operations, and most infrastructure has been removed from the site. The closure comes as a result of their lease ending. Beginning in the 18th century, northern elephant seals ( Mirounga angustirostris ) were hunted extensively almost to extinction by the end of the 19th century. They were prized for oil that could be made from their blubber , and
14976-454: 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. It was formed by a transform boundary. The southern segment (also known as the Mojave segment) begins near Bombay Beach, California . Box Canyon, near
15104-526: The specific populations to be hardest impacted by a potential earthquake of a 7.0 magnitude, specifically in the San Francisco Bay Area. This includes intensified hardships for those with low-income, racially and culturally-diverse populations, and people with literacy hardships that would significantly "increase their risk of displacement and add to recovery challenges" (Wein et al.). In addition to societal and landscape impacts, this study looks at potential business interruptions. This portion estimates impacts to
15232-546: The stage for confusion and lengthy court battles when the rancho was dissolved. Unlike many rancheros, Garcia obeyed the law by actually living there. He built a wood and thatch home near what is now the National Seashore's Bear Valley Headquarters and soon had a home for his family as well as a headquarters for his extensive ranching operation which consisted of approximately 3,000 cattle, 400 horses, and large herds of sheep and hogs. When Mexico lost California to
15360-411: The study, Fialko stated: All these data suggest that the fault is ready for the next big earthquake but exactly when the triggering will happen and when the earthquake will occur we cannot tell. It could be tomorrow or it could be 10 years or more from now. Nevertheless, in the 18 years since that publication there has not been a substantial quake in the Los Angeles area, and two major reports issued by
15488-552: The survey and daunting legal fees. Entrepreneurial Americans were delighted to capitalize on the opportunity. With cash in hand, they purchased these huge Mexican land grants, often paying less than $ 2 per acre, thus beginning Point Reyes's next chapter as a dairying empire. Settlement patterns at Point Reyes were forever changed when the Shafters acquired it in 1857. Brothers Oscar Lovell Shafter and James McMillan Shafter established large-scale successful dairy operations. 13 of
15616-468: The term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along
15744-464: The time of European arrival were the Coast Miwok . They left evidence of well over a hundred encampments on the peninsula, with a population estimated to have been nearly 3,000. Seasonal hunters and gatherers, they were nourished by fish, clams, mussels, and crab, in addition to the deer, elk, bear, mud hen, geese, and small game they hunted with spears and bows. The Coast Miwok utilized a variety of different plants growing at Point Reyes. Acorns served as
15872-484: Was 2.65 inches (67 mm) on December 15, 1929. Automated weather observations are now taken at the lighthouse. Weather observations are also taken in nearby Point Reyes Station and published in local newspapers, including the San Francisco Chronicle . It can get very foggy and windy during certain parts of the year at the lighthouse, and to be effective, the lighthouse had to be situated below
16000-436: Was 90 °F (32 °C) on October 3, 1917, and the lowest temperature recorded was 31 °F (−1 °C) on January 19, 1922. Annual precipitation averaged 17.05 inches (433 mm). The wettest year on record was 1941 with 31.37 inches (797 mm) and the driest year was 1923 was 7.32 inches (186 mm). The most precipitation in one month was 9.51 inches (242 mm) in December 1916. The maximum 24-hour precipitation
16128-414: Was a cow pasture. By 1880, it had a hotel, saloon, blacksmith shop, livery stable, butcher shop, and school. Its post office was completed in 1882, and its first store opened in 1883. When the railroad era ended, growth was slow. It was not until after World War II that a medical center and a shopping center, including a drugstore, dentist, coffee shop, and library, had been completed. The train station became
16256-508: Was discovered on a sheltered beach below Point Reyes' Chimney Rock in 1981 and has multiplied at a remarkable 16% per year to the present population of 1,500 to 2,000 individuals each winter. California's native tule elk ( Cervus canadensis nannodes ) were hunted until only a handful of animals remained in California's southern Central Valley . Joseph Warren Revere , the grandson of Revolutionary War patriot Paul Revere , wrote in his book Naval Duty in California that he counted 400 elk in
16384-509: Was used by American, British, and Russian smugglers intent on avoiding tariffs and regulations. Later, when the Gold Rush of 1849 generated a huge market for lumber, Bolinas became the port for nearby timber operations and, briefly, quarrying limestone. By the late 1960s, Bolinas had become home to a large community of hippies, many of whom had left San Francisco's Haight-Ashbury for a less populated paradise. In 1971, they succeeded in scrapping
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