Oceanography known as oceanology, is the study of the physical and biological aspects of the ocean. It is an important Earth science, which covers a wide range including ecosystem dynamics; these diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean and understanding of processes within: astronomy, chemistry, geography, hydrology and physics. Paleoceanography studies the history of the oceans in the geologic past. Humans first acquired knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides were recorded by Strabo. Early exploration of the oceans was for cartography and limited to its surfaces and of the animals that fishermen brought up in nets, though depth soundings by lead line were taken. Although Juan Ponce de León in 1513 first identified the Gulf Stream, the current was well known to mariners, Benjamin Franklin made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and explained the Gulf Stream's cause.
Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769–1770. Information on the currents of the Pacific Ocean was gathered by explorers of the late 18th century, including James Cook and Louis Antoine de Bougainville. James Rennell wrote the first scientific textbooks on oceanography, detailing the current flows of the Atlantic and Indian oceans. During a voyage around the Cape of Good Hope in 1777, he mapped "the banks and currents at the Lagullas", he was the first to understand the nature of the intermittent current near the Isles of Scilly. Sir James Clark Ross took the first modern sounding in deep sea in 1840, Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831–1836. Robert FitzRoy published a four-volume report of Beagle's three voyages. In 1841 -- 1842 Edward Forbes undertook dredging in the Aegean Sea; the first superintendent of the United States Naval Observatory, Matthew Fontaine Maury devoted his time to the study of marine meteorology and charting prevailing winds and currents.
His 1855 textbook Physical Geography of the Sea was one of the first comprehensive oceanography studies. Many nations sent oceanographic observations to Maury at the Naval Observatory, where he and his colleagues evaluated the information and distributed the results worldwide. Despite all this, human knowledge of the oceans remained confined to the topmost few fathoms of the water and a small amount of the bottom in shallow areas. Nothing was known of the ocean depths; the British Royal Navy's efforts to chart all of the world's coastlines in the mid-19th century reinforced the vague idea that most of the ocean was deep, although little more was known. As exploration ignited both popular and scientific interest in the polar regions and Africa, so too did the mysteries of the unexplored oceans; the seminal event in the founding of the modern science of oceanography was the 1872–1876 Challenger expedition. As the first true oceanographic cruise, this expedition laid the groundwork for an entire academic and research discipline.
In response to a recommendation from the Royal Society, the British Government announced in 1871 an expedition to explore world's oceans and conduct appropriate scientific investigation. Charles Wyville Thompson and Sir John Murray launched the Challenger expedition. Challenger, leased from the Royal Navy, was modified for scientific work and equipped with separate laboratories for natural history and chemistry. Under the scientific supervision of Thomson, Challenger travelled nearly 70,000 nautical miles surveying and exploring. On her journey circumnavigating the globe, 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken. Around 4,700 new species of marine life were discovered; the result was the Report Of The Scientific Results of the Exploring Voyage of H. M. S. Challenger during the years 1873–76. Murray, who supervised the publication, described the report as "the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries".
He went on to found the academic discipline of oceanography at the University of Edinburgh, which remained the centre for oceanographic research well into the 20th century. Murray was the first to study marine trenches and in particular the Mid-Atlantic Ridge, map the sedimentary deposits in the oceans, he tried to map out the world's ocean currents based on salinity and temperature observations, was the first to understand the nature of coral reef development. In the late 19th century, other Western nations sent out scientific expeditions; the first purpose built oceanographic ship, was built in 1882. In 1893, Fridtjof Nansen allowed Fram, to be frozen in the Arctic ice; this enabled him to obtain oceanographic and astronomical data at a stationary spot over an extended period. In 1881 the geographer John Francon Williams published Geography of the Oceans. Between 1907 and 1911 Otto Krümmel published the Handbuch der Ozeanographie, which became influential in awakening public interest in oceanography.
Gulf of California
The Gulf of California is a marginal sea of the Pacific Ocean that separates the Baja California Peninsula from the Mexican mainland. It is bordered by the states of Baja California, Baja California Sur and Sinaloa with a coastline of 4,000 km. Rivers which flow into the Gulf of California include the Colorado, Mayo, Sinaloa and the Yaqui; the gulf's surface area is about 160,000 km2. Depths range from fording at the estuary near Yuma, Arizona, to in excess of 3,000 meters in the deepest parts; the Gulf is thought to be one of the most diverse seas on the planet, is home to more than 5,000 species of micro-invertebrates. Home to over a million people, Baja California is the second-longest peninsula in the world, after the Malay Peninsula in Southeast Asia. Parts of the Gulf of California are a UNESCO World Heritage Site. AreaThe International Hydrographic Organization defines the southern limit of the Gulf of California as: "A line joining Piastla Point in Mexico, the southern extreme of Lower California".
The Gulf of California is 1,126 km long and 48–241 km wide, with an area of 177,000 km2, a mean depth of 818.08 m, a volume of 145,000 km3. The Gulf of California includes three faunal regions: the Northern Gulf of California the Central Gulf of California the Southern Gulf of CaliforniaOne recognized transition zone is termed the Southwestern Baja California Peninsula. Transition zones exist between faunal regions, they vary for each individual species. Geology Geologic evidence is interpreted by geologists as indicating the Gulf of California came into being around 5.3 million years ago as tectonic forces rifted the Baja California Peninsula off the North American Plate. As part of this process, the East Pacific Rise propagated up the middle of the Gulf along the seabed; this extension of the East Pacific Rise is referred to as the Gulf of California Rift Zone. The Gulf would extend as far as Indio, except for the tremendous delta created by the Colorado River; this delta blocks the sea from flooding the Imperial Valleys.
Volcanism dominates the East Pacific Rise. The island of Isla Tortuga is one example of this ongoing volcanic activity. Furthermore, hydrothermal vents due to extension tectonic regime, related to the opening of the Gulf of California, are found in the Bahía de Concepción, Baja California Sur. Islands The Gulf of California contains 37 major islands – the two largest being Isla Ángel de la Guarda and Tiburón Island. Most of the islands are found on the peninsular side of the gulf. In fact, many of the islands of the Sea of Cortez are the result of volcanic explosions that occurred during the early history of Baja California; the islands of Islas Marías, Islas San Francisco, Isla Partida are thought to be the result of such explosions. The formations of the islands, are not dependent on each other, they were each formed as a result of an individual structural occurrence. Several islands, including Isla Coronados, are home to volcanoes; the gulf has islands which together total about 420 hectares.
All of them as a whole were enacted as "Area Reserve and Migratory Bird Refuge and Wildlife" on August 2, 1978. In June 2000, the islands were given a new category "Protection Area Wildlife". In addition to this effort by the Mexican government, for its importance and recognition worldwide, all islands in the Gulf of California are part of the international program "Man and Biosphere" and are part of the World Reserve Network UNESCO Biosphere as Special Biosphere Reserve. Due to the vast expanse covered by this federal protected area conservation and management is carried out through a system of four regional directorates by way of co-direction. There is a regional directorate in the states of Baja California, Baja California Sur and Sinaloa. Notwithstanding the foregoing, the work of direct and indirect conservation is done in the islands is governed by a single Management Program, published in 2000, complemented by local and specific management programs archipelagos; the Directorate of Protection Area Wildlife California Gulf Islands in Baja California is responsible for 56 islands located off the coast of the state.
These are grouped into four archipelagos: San Luis Gonzaga or Enchanted, Guardian Angel, Bahia de los Angeles and San Lorenzo. Shores and tidesThe three general types of shores found in the Gulf of California include rocky shore, sandy beach, tidal flat; some of the rich biodiversity and high endemism that characterize the Gulf of California and make it such a hotspot for fishing can be attributed to insignificant factors, such as the types of rocks that make up a shore. Beaches with softer, more porous rocks have a higher species richness than those with harder, smoother rocks. Porous rocks will have more cracks and crevices in them, making them ideal living spaces for many animals; the rocks themselves, however need to be stable on the shore for a habitat to be stable. Additionally, the color of the rocks can affect the organisms living on a shore. For example, darker rocks will be warmer than lighter ones, can deter animals that do not have a high tolerance for heat. The
Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, since tectonic processes began on Earth between 3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century; the geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. The lithosphere, the rigid outermost shell of a planet, is broken into tectonic plates; the Earth's lithosphere is composed of many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, oceanic trench formation occur along these plate boundaries; the relative movement of the plates ranges from zero to 100 mm annually. Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust.
Along convergent boundaries, subduction, or one plate moving under another, carries the lower one down into the mantle. In this way, the total surface of the lithosphere remains the same; this prediction of plate tectonics is referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual expansion of the globe. Tectonic plates are able to move because the Earth's lithosphere has greater mechanical strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography and density changes in the crust. At subduction zones the cold, dense crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell. Another explanation lies in the different forces generated by tidal forces of the Moon; the relative importance of each of these factors and their relationship to each other is unclear, still the subject of much debate.
The outer layers of the Earth are divided into the asthenosphere. The division is based on differences in mechanical properties and in the method for the transfer of heat; the lithosphere is more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere transfers heat by convection and has a nearly adiabatic temperature gradient; this division should not be confused with the chemical subdivision of these same layers into the mantle and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like asthenosphere. Plate motions range up to a typical 10–40 mm/year, to about 160 mm/year; the driving mechanism behind this movement is described below. Tectonic lithosphere plates consist of lithospheric mantle overlain by one or two types of crustal material: oceanic crust and continental crust.
Average oceanic lithosphere is 100 km thick. Because it is formed at mid-ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid-ocean ridge where it was formed. For a typical distance that oceanic lithosphere must travel before being subducted, the thickness varies from about 6 km thick at mid-ocean ridges to greater than 100 km at subduction zones. Continental lithosphere is about 200 km thick, though this varies between basins, mountain ranges, stable cratonic interiors of continents; the location where two plates meet is called a plate boundary. Plate boundaries are associated with geological events such as earthquakes and the creation of topographic features such as mountains, mid-ocean ridges, oceanic trenches; the majority of the world's active volcanoes occur along plate boundaries, with the Pacific Plate's Ring of Fire being the most active and known today. These boundaries are discussed in further detail below; some volcanoes occur in the interiors of plates, these have been variously attributed to internal plate deformation and to mantle plumes.
As explained above, tectonic plates may include continental crust or oceanic crust, most plates contain both. For example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans; the distinction between oceanic crust and continental crust is based on their modes of formation. Oceanic crust is fo
Soquel Canyon State Marine Conservation Area
Soquel Canyon State Marine Conservation Area is an offshore marine protected area in Monterey Bay. Monterey Bay is on California’s central coast with the city of Monterey at its south end and the city of Santa Cruz at its north end; the SMCA covers 23.41 square miles. Within the SMCA, fishing and taking of any living marine resources is prohibited except the commercial and recreational take of pelagic finfish. Soquel Canyon SMCA was established in September 2007 by the California Department of Game, it was one of 29 marine protected areas adopted during the first phase of the Marine Life Protection Act Initiative. The Marine Life Protection Act Initiative is a collaborative public process to create a statewide network of marine protected areas along the California coastline; the Soquel Canyon SMCA captures an entire side-branch of the Monterey Submarine Canyon. This marine protected area is bounded by straight lines connecting the points: 36°51′N 121°56′W 36°51′N 122°3.8′W 36°48′N 122°2.88′W 36°48′N 121°56′W The Monterey Submarine Canyon is a unique and biologically productive habitat.
The rocky canyon walls and mud-and-sand canyon floor offer ideal habitat for rockfishes including depleted species. It sponges; the area is an important seabird forage ground and whale feeding area. The natural environment and ocean resources of the Monterey Peninsula draw millions of visitors from around the world each year, including more than 65,000 scuba divers drawn by the area's easy access, variety of wildlife, kelp forests; the Monterey Bay Aquarium is a tourist attraction featuring a 28-foot deep living kelp forest. The exhibit includes many of the species native to the nearby marine protected areas; the aquarium houses sea otters, intertidal wildlife, sea turtles. In addition to diving and visiting the aquarium, people visit Monterey Bay for kayaking, whale watching, charter fishing, bird watching and walking on the beach. California's marine protected areas encourage educational uses of the ocean. Activities such as kayaking, diving and swimming are allowed unless otherwise restricted.
Click here for a virtual tour of the MPA As specified by the Marine Life Protection Act, select marine protected areas along California’s central coast are being monitored by scientists to track their effectiveness and learn more about ocean health. Similar studies in marine protected areas located off of the Santa Barbara Channel Islands have detected gradual improvements in fish size and number. Local scientific and educational institutions involved in the monitoring include Stanford University’s Hopkins Marine Station, University of California Santa Cruz, Moss Landing Marine Laboratories and Cal Poly San Luis Obispo. Research methods include hook-and-line sampling and scuba diver surveys, the use of Remote Operated Vehicle submarines. California MPA information Monterey Bay Aquarium Marine Life Protection Act Initiative CalOceans
Central Valley (California)
The Central Valley is a flat valley that dominates the geographical center of the U. S. state of California. It is 40 to 60 miles wide and stretches 450 miles from north-northwest to south-southeast, inland from and parallel to the Pacific Ocean coast, it covers 18,000 square miles, about 11% of California's total land area. The valley is bounded by the Sierra Nevada to the Coast Ranges to the west, it is California's single most productive agricultural region and one of the most productive in the world, providing more than half of the fruits and nuts grown in the United States. More than 7 million acres of the valley are irrigated via an extensive system of reservoirs and canals; the valley has many major cities, including the state capital Sacramento. The Central Valley watershed comprises over a third of California, it consists of three main drainage systems: the Sacramento Valley in the north, which receives well over 20 inches of rain annually. The Sacramento and San Joaquin river systems drain their respective valleys and meet to form the Sacramento–San Joaquin River Delta, a large expanse of interconnected canals, stream beds, sloughs and peat islands.
The delta empties into the San Francisco Bay, ultimately flows into the Pacific. The waters of the Tulare Basin never flow to the ocean, though they are connected by man-made canals to the San Joaquin and could drain there again if they were to rise high enough; the valley encompasses all or parts of 18 Northern California counties: Butte, Glenn, Kings, Merced, San Joaquin, Shasta, Stanislaus, Tehama, Yuba and the Southern California county of Kern. The Central Valley is known to residents as "the Valley." Older names include "the Great Valley," a name still seen in scientific references, "Golden Empire," a booster name, still referred to by some organizations. The Central Valley is outlined by the Cascade, Sierra Nevada, Tehachapi mountain ranges on the east, the California Coast Ranges and San Francisco Bay on the west; the broad valley floor is carpeted by vast agricultural regions, dotted with numerous population centers. Subregions and their counties associated with the valley include: North Sacramento Valley Sacramento Metro North San Joaquin South San Joaquin There are four main population centers in the Central Valley, each equidistant from the next, from south to north: Bakersfield, Fresno and Redding.
While there are many communities large and small between these cities, these four cities act as hubs for regional commerce and transportation. About 6.5 million people live in the Central Valley today, it is the fastest growing region in California. There are 12 Metropolitan Statistical Areas and 1 Micropolitan Statistical Area in the Central Valley. Below, they are listed by μSA population; the largest city is the state capital Sacramento, followed by Fresno. The following metropolitan and micropolitan statistical areas listed from largest to smallest: The flatness of the valley floor contrasts with the rugged hills or gentle mountains that are typical of most of California's terrain; the valley is thought to have originated below sea level as an offshore area depressed by subduction of the Farallon Plate into a trench further offshore. The San Joaquin Fault is a notable seismic feature of the Central Valley; the valley was enclosed by the uplift of the Coast Ranges, with its original outlet into Monterey Bay.
Faulting moved the Coast Ranges, a new outlet developed near what is now San Francisco Bay. Over the millennia, the valley was filled by the sediments of these same ranges, as well as the rising Sierra Nevada to the east; the one notable exception to the flat valley floor is Sutter Buttes, the remnants of an extinct volcano just to the northwest of Yuba City, 44 miles north of Sacramento. Another significant geologic feature of the Central Valley lies hidden beneath the delta; the Stockton Arch is an upwarping of the crust beneath the valley sediments that extends southwest to northeast across the valley. The Central Valley lies within the California Trough physiographic section, part of the larger Pacific Border province, which in turn is part of the Pacific Mountain System; the "Central Valley grassland" is the Nearctic temperate and subtropical grasslands and shrub lands ecoregion, once a diverse grassland containing areas of desert grassland, savanna, riverside woodland, several types of seasonal vernal pools, large lakes such as now-dry Tulare Lake, Buena Vista Lake and Kern Lake.
However, much of the Central Valley environment
Longshore drift from longshore current is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, dependent on oblique incoming wind direction. Oblique incoming wind squeezes water along the coast, so generates a water current which moves parallel to the coast. Longshore drift is the sediment moved by the longshore current; this current and sediment movement occur within the surf zone. Beach sand is moved on such oblique wind days, due to the swash and backwash of water on the beach. Breaking surf sends water up the beach at an oblique angle and gravity drains the water straight downslope perpendicular to the shoreline, thus beach sand can move downbeach in a zig zag fashion many tens of meters per day. This process is called "beach drift" but some workers regard it as part of "longshore drift" because of the overall movement of sand parallel to the coast. Longshore drift affects numerous sediment sizes as it works in different ways depending on the sediment.
Sand is affected by the oscillatory force of breaking waves, the motion of sediment due to the impact of breaking waves and bed shear from long-shore current. Because shingle beaches are much steeper than sandy ones, plunging breakers are more to form, causing the majority of long shore transport to occur in the swash zone, due to a lack of an extended surf zone. There are numerous calculations that take into consideration the factors that produce longshore drift; these formulations are: Bijker formula Bijker formula The Engelund and Hansen formula The Ackers and White formula The Bailard and Inman formula The Van Rijn formula The Watanabe formula These formulas all provide a different view into the processes that generate longshore drift. The most common factors taken into consideration in these formulas are: Suspended and bed load transport Waves e.g. breaking and non-breaking The shear exerted by waves or the flow associated with waves. Longshore drift plays a large role in the evolution of a shoreline, as if there is a slight change of sediment supply, wind direction, or any other coastal influence longshore drift can change affecting the formation and evolution of a beach system or profile.
These changes do not occur due to one factor within the coastal system, in fact there are numerous alterations that can occur within the coastal system that may affect the distribution and impact of longshore drift. Some of these are: e.g. erosion, backshore changes and emergence of headlands. Change in hydrodynamic forces, e.g. change in wave diffraction in headland and offshore bank environments. Change deltas on drift. Alterations of the sediment budget, e.g. switch of shorelines from drift to swash alignment, exhaustion of sediment sources. The intervention of humans, e.g. cliff protection, detached breakwaters. By the Hydrogenic order of the atoms from water, Nathan James Heenan has proved in 1924 that water itself without force of wind can destroy or add deposition to the sea beds, we can find this out by the equation: H2o x force of water - Amount of H2 The sediment budget takes into consideration sediment sources and sinks within a system; this sediment can come from any source with examples of sources and sinks consisting of: Rivers Lagoons Eroding land sources Artificial sources e.g. nourishment Artificial sinks e.g. mining/extraction Offshore transport Deposition of sediment on shore Gullies through the landThis sediment enters the coastal system and is transported by longshore drift.
A good example of the sediment budget and longshore drift working together in the coastal system is inlet ebb-tidal shoals, which store sand, transported by long-shore transport. As well as storing sand these systems may transfer or by pass sand into other beach systems, therefore inlet ebb-tidal systems provide a good sources and sinks for the sediment budget. Sediment deposition throughout a shoreline profile conforms to the null point hypothesis. Long shore occurs in a 90 to 80 degree backwash so it would be presented as a right angle with the wave line; this section consists of features of longshore drift that occur on a coast where long-shore drift occurs uninterrupted by man-made structures. Spits are formed when longshore drift travels past a point where the dominant drift direction and shoreline do not veer in the same direction; as well as dominant drift direction, spits are affected by the strength of wave driven current, wave angle and the height of incoming waves. Spits are landforms that have two important features, with the first feature being the region at the up-drift end or proximal end.
The proximal end is attached to land and may form a slight “barrier” between the sea and an estuary or lagoon. The second important spit feature is the down-drift end or distal end, detached from land and in some cases, may take a complex hook-shape or curve, due to the influence of varying wave directions; as an example, the New Brighton spit in Canterbury, New Zealand, was created by longshore drift of sediment from the Waimakariri River to the north. This spit system is in equilibrium but undergoes alternate phases of deposition and erosion. Barrier systems are attached to the land at both the proximal and distal end and are generally
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