Geology Of California
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The geology of
California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
is highly complex, with numerous mountain ranges, substantial
faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
and tectonic activity, rich
natural resources Natural resources are resources that are drawn from nature and used with few modifications. This includes the sources of valued characteristics such as commercial and industrial use, aesthetic value, scientific interest and cultural value. O ...
and a history of both ancient and comparatively recent intense geological activity. The area formed as a series of small
island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...
s, deep-ocean sediments and
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
oceanic crust accreted to the western edge of
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, producing a series of deep basins and high mountain ranges. One of the most important events was the advent of the
San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...
around 29 million years ago in the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
, when the region
subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
a spreading center in the
East Pacific Rise The East Pacific Rise is a mid-ocean rise (termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), a divergent tectonic plate boundary located along ...
. This produced major crustal stretching, volcanism and displacement of up to 125 miles.


Geological history

The oldest rocks in California date back 1.8 billion years to the
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
and are found in the
San Gabriel Mountains The San Gabriel Mountains ( es, Sierra de San Gabriel) are a mountain range located in northern Los Angeles County, California, Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Tr ...
,
San Bernardino Mountains The San Bernardino Mountains are a high and rugged mountain range in Southern California in the United States. Situated north and northeast of San Bernardino and spanning two California counties, the range tops out at at San Gorgonio Mountain â ...
, and
Mojave Desert The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily in ...
. The rocks of eastern California formed a shallow continental shelf, with massive deposition of
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
during the
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
, and sediments from this time are common in the
Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...
,
Klamath Mountains The Klamath Mountains are a rugged and lightly populated mountain range in northwestern California and southwestern Oregon in the western United States. As a mountain system within both the greater Pacific Coast Ranges and the California Coast R ...
and eastern
Transverse Range The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa B ...
. Active
subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
began in the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
during the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
, producing large
granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
intrusions and the beginning of the
Nevadan Orogeny The Nevadan orogeny occurred along the western margin of North America during the Middle Jurassic to Early Cretaceous time which is approximately from 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different kin ...
as well as more dryland conditions and the retreat of the ocean to the west. Throughout the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
the Nevadan Orogeny accelerated with large-scale granitic intrusions and erosion into deep marine basins. These basins steadily filled with sediment, with one famous example preserved as the Great Valley beds in the Coast Ranges. Simultaneously island arcs and small sections of continental crust rafted onto the edge of North America, building out the continent. During the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
, the volcanic and deep water sedimentary Franciscan rocks were accreted to the edge of California and vast areas of marine sedimentary rocks deposited in the Central Valley and what would become the Transverse and Coast Ranges. Examples of filled basins included the Los Angeles Basin, the Eel River Basin around Eureka or the 50,000 foot thick sedimentary sequences of the Ventura Basin. The San Andreas Fault became perhaps most active after the
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
, potentially resulting in up to 350 miles of offset in some locations.


Regional geology


California Coast Ranges

The
California Coast Ranges The Coast Ranges of California span from Del Norte or Humboldt County, California, south to Santa Barbara County. The other three coastal California mountain ranges are the Transverse Ranges, Peninsular Ranges and the Klamath Mountains. P ...
extend from the Oregon line southward 600 miles to the
Santa Ynez River The Santa Ynez River is one of the largest rivers on the Central Coast of California. It is long, ArcExplorer GIS data viewer. flowing from east to west through the Santa Ynez Valley, reaching the Pacific Ocean at Surf, near Vandenberg Space Fo ...
. The mountains are drained by the
Russian Russian(s) refers to anything related to Russia, including: *Russians (, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (), Russian language term for all citizens and peo ...
,
Eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
, Mad and
Klamath Klamath may refer to: Ethnic groups *Klamath people, a Native American people of California and Oregon **Klamath Tribes, a federally recognized group of tribes in Oregon *Klamath language, spoken by the Klamath people Places in the United States * ...
rivers which tend to follow faults and folds. Per square mile of drainage, the Eel River has the highest suspended sediment load of any river in the US, exceeding the Colorado River and Mississippi River. The Franciscan subduction complex makes up the basement rock for part of the range, with a
mélange In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically cons ...
dominated by
graywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
first deposited in offshore deep ocean basins. These rocks are rich in plagioclase, quartz and chlorite mica (which gives them a greenish color) and range up to 25,000 feet thick. In some places they are interbedded with shale, limestone and
radiolarian The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The elab ...
chert. Examples of rock formations in the Franciscan subduction complex include the Calera limestone east of the San Andreas fault or the Laytonville limestone which extends north of San Francisco to Eureka. Franciscan rocks have a complex geological structure. In some places,
ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found i ...
sequences preserve remnant
oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...
rock on land, while other parts of the range are intruded with ultrabasic igneous rocks that have serpentinized to
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...
. In the southern part of the range, between the Nacimiento and San Andreas fault zones, the metamorphic rocks and granite plutons of the Salinian block make up the basement rock. These rocks were likely moved to their current location by the two major faults. Some Great Valley rocks are exposed in the Coastal Ranges as well, like the Jurassic Knoxville Formation shale. Sur Series schist, quartzite, marble, gneiss and granulite in the Salinian block likely deposited in a marine shelf late in the
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
. Shelf and slope deposits would ultimately become Great Valley rocks, while the trench deposits became the Franciscan subduction complex. Major geologic changes began in the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
with continued continental shelf deposition of shale, sandstone and clay as well as near-shore tropical coal deposits. During the Miocene, the Coast Ranges were flooded again, with underwater volcanic eruptions in the southern part of the range and deposition of fossil-rich shales like the Monterey formation. Uplift took place into the Pliocene and Pleistocene, slowly reducing sea levels inland in the Central Valley. The Coast Range is at even higher risk for damaging landslides than other parts of coastal California due to sheared serpentinite in Franciscan basement rocks.


Central Valley

The Central Valley includes the southern
San Joaquin Valley The San Joaquin Valley ( ; es, Valle de San Joaquín) is the area of the Central Valley of the U.S. state of California that lies south of the Sacramento–San Joaquin River Delta and is drained by the San Joaquin River. It comprises seven c ...
and the northern
Sacramento Valley , photo =Sacramento Riverfront.jpg , photo_caption= Sacramento , map_image=Map california central valley.jpg , map_caption= The Central Valley of California , location = California, United States , coordinates = , boundaries = Sierra Nevada (ea ...
. The
Great Valley Sequence The Great Valley Sequence of California is a -thick group of related geologic formations that are Late Jurassic through Cretaceous in age (150–65 Ma) on the geologic time scale. These sedimentary rocks were deposited during the late Mesozoic ...
is a 40,000 foot thick formation at the western edge of the Central Valley that formed between the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, overlying the
Franciscan Assemblage The Franciscan Complex or Franciscan Assemblage is a geologic term for a late Mesozoic terrane of heterogeneous rocks found throughout the California Coast Ranges, and particularly on the San Francisco Peninsula. It was named by geologist Andrew ...
and granite rocks associated with the
Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...
to the east. It represents an ancient
forearc basin Forearc is a plate tectonic term referring to a region between an oceanic trench, also known as a subduction zone, and the associated volcanic arc. Forearc regions are present along a convergent margins and eponymously form 'in front of' the vol ...
that took shape as oceanic crust subducted under the west edge of the continent. During the Jurassic, many sediments shed into the region from the rising proto-Sierra Nevada. For much of the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
the region was filled with lakes and brackish swamps. Thick
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
sediments formed in narrow seaways from the Pacific. The Stockton fault and White Wolf fault by Bakersfield are both major tectonic features. The 7.6 magnitude
1952 Kern County earthquake The 1952 Kern County earthquake occurred on July 21 in the southern San Joaquin Valley and measured 7.3 on the moment magnitude scale. The main shock occurred at 4:52 am Pacific Daylight Time (11:52 UTC), killed 12 people, injured hundreds mor ...
was one of the most powerful in California in the 20th century. The subsurface is well known from oil wells and oil fields are bounded in the east by the Kern Front fault. A small andesitic dome near Marysville is the only example of volcanic rocks in the valley exposed near the surface.


Coronado Island

The distinctive Coronado Island in San Diego County helps to create the large sheltered harbor of San Diego. It formed as a sandspit filled in to the north from sediment deposited by the Tijuana River and sheltered from wind and waves by the Cretaceous uplands of Point Loma. Two small islands to the north: North Island and South Island have been connected with fill to create the Naval Air Station. Without continuous dredging, San Diego Bay would fill with sediment and become dry land with deposition from the San Diego, Sweetwater and Otay rivers.


Klamath Mountains

The Klamath Mountains formed as small island arc terranes accreted against the coast of North America before and during the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
and overlain by newer rocks, deposited from the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
to modern times. Geologists have subdivided the four terranes in the mountain range, referring to them as "plates." The Klamath Mountains have several areas of preserved oceanic crust. The Josephine ophiolite forms the basement of the western Klamath Mountains, with extensive
peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high prop ...
from the boundary between the oceanic crust and the mantle, as well as chromite and nickel deposits. It is exposed in the Smith River drainage to the north of US Highway 199 in
Del Norte County ), in California , seat_type = County seat , seat = Crescent City , parts_type = Largest city , parts = Crescent City , unit_pref = US , area_total_sq_mi = 1230 , area_land_sq_mi = 1006 , area_water_sq_mi = 223 , elevation_max_footnote ...
. By contrast, the Trinity ophiolite is found in the east, known for its numerous ultramafic rocks and being one of the most extensive ophiolites in the US. The Western Jurassic Plate stretches for 220 miles on the western edge of the mountains. The thick Galice formation
slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...
and metamorphosed
greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...
overlie the Josephine ophiolite and likely deposited in a deep ocean environment offshore of the island arc. It also interfingers with up 23,000 feet of volcanic rocks in the Rogue Formation. Some rocks in the Western Jurassic Plate seem to have been subducted, reaching
blueschist Blueschist (), also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (), approximately corresponding to a depth of . The blue co ...
grade metamorphism in the sequence of
metamorphic facies A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.Essentials of Geology, 3rd Edition, Stephen Marshak The assemblage is typical of what is formed in conditions corresponding ...
in the South Fork Mountain schist. By contrast, the Eastern Klamath Plate is made up of limestone, chert and pyroclastic rocks, divided in half by the Trinity ophiolite. A thrust fault, known as the Trinity or Bully Choop thrust, separates the Eastern Klamath Plate from the Central Metamorphic Plate. This region of the mountains was likely underthrusted by the adjoining plates, producing multiple schists around 380 to 400 million years ago in the
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
. Many of these schists, like the Condrey Mountain schist are more resistant to erosion than other rocks close by. The Western Paleozoic and Triassic Plate is the most common unit of the Klamath Mountains and is up to 50 miles wide at the Oregon state line. Geologists have struggled to define its structural geology with complex sequences of deep ocean crust, upper mantle rock and tectonic melanges. Granite plutons emplaced during the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, forming rock units like the Ironside Mountain diorite, which outcrops for 37 miles from the Orleans Mountain lookout tower to the line between Humboldt County and Siskiyou County or the Shasta Bally batholith at Buckhorn Summit west of Redding. A few may date earlier, like the 400 million year old Mule Mountain. During the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
, the mountains had a large number of glaciers and
cirques A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...
and glacially-carved U-shaped valleys are remaining features from that time period. Large boulders have often eroded out of moraine deposits, coming to rest a few miles away. Fast flowing rivers meant that the region has accumulated very little alluvium, except for a rare 400 foot thick deposit in Scott Valley, southwest of
Yreka Yreka ( ) is the county seat of Siskiyou County, California, United States, near the Shasta River; the city has an area of about , most of it land. As of the 2020 United States Census, the population was 7,807, reflecting a meager increase fro ...
, California.


Modoc Plateau

The Modoc Plateau is an undulating expanse of Miocene to Holocene basalt law flows at the southwest edge of the Columbia Plateau, covering 10,000 square miles. It is drained by the Pit River, which ultimately reaches Shasta Lake and the Sacramento River. The Warner Basalt is the most common rock in the plateau, bordered by the Surprise Valley fault zone that first became active in the Miocene 15 million years ago. Based on faulting in recent alluvial material, the Surprise Valley fault zone is still active. In spite of low rainfall, the numerous lava tubes and volcanic fractures in the plateau produce the Fall River Springs, one of the largest springs in the US. At least 300 lava tubes are known in
Lava Beds National Monument Lava Beds National Monument is located in northeastern California, in Siskiyou and Modoc counties. The monument lies on the northeastern flank of Medicine Lake Volcano and has the largest total area covered by a volcano in the Cascade Range. ...
, some of which preserve ice year round. The rugged terrain of the Modoc Plateau played an important role in the
Modoc War The Modoc War, or the Modoc Campaign (also known as the Lava Beds War), was an armed conflict between the Native American Modoc people and the United States Army in northeastern California and southeastern Oregon from 1872 to 1873. Eadweard Mu ...
. In 1873, 53 Modoc men held off 650 US troops, killing 70 of them in heavy weather in the lava plateau to the south of Tule Lake. The Modoc exploited collapse pits and lava tunnels, turning to Tule Lake for food (subsequent drainage has reduced the lake shoreline).


Mojave Desert

The
Mojave Desert The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily in ...
extends into areas of
Basin and Range Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...
terrain and includes some of the oldest rocks exposed at the surface in California. The movement of the San Andreas Fault and
Garlock Fault The Garlock Fault is a left-lateral strike-slip fault running northeast–southwest along the north margins of the Mojave Desert of Southern California, for much of its length along the southern base of the Tehachapi Mountains. Geography Stretc ...
helped to induce arid conditions during the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
. Unlike most of California, the Mojave region has numerous
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pêž’, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
rocks, such as granitic gneiss or marble intruded with porphyry in the
Ord Mountains The Ord Mountains are located in the Mojave Desert of southern California, USA. The range lies in a generally east–west direction, and reaches an elevation of above sea level at East Ord Mountain. The range is approximately long, and is about ...
or schist in the Old Woman Mountains. The Marble Mountain
Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, êž’) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...
lies unconformably atop Proterozoic granites. During the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
high sea levels retreated, switching to the deposition of the terrestrial Aztec sandstone. Volcanic rocks erupted around Barstow in the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
. Lake beds interbedded with volcanic ash are typical of the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
. Volcanism continued through the
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
, forming the 300 foot thick basalts of the Cima Volcanic Field or the Barstow-Amboy axis of volcanic craters, which have protected underlying granite from erosion. Unique geology in the region formed bastnaesite mined at the Mountain Pass rare earth mine. Additionally,
borate A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also refe ...
deposited during arid conditions, with mining after 1926.


Newport Bay

At the edge of the Los Angeles coastal plain and just west of the San Joaquin Hills, Newport Bay is a major hub of boating. Geologists have interpreted the bay as the drowned channel of the Santa Ana River. Flow in and out of the estuary has been controlled with a man-made structure since heavy silting in 1915. Virtually all of the islands in the bay are man-made from dredged sediments. However, a bulge in the bay's sand spit records offshore presence of the Newport submarine canyon. In the 19th century, a railroad pier was built out into the canyon to avoid waves closer in to shore when loading and unloading ships.


Peninsular Ranges

The
Peninsular Ranges The Peninsular Ranges (also called the Lower California province) are a group of mountain ranges that stretch from Southern California to the southern tip of the Baja California peninsula; they are part of the North American Coast Ranges, which ...
are a group of mountain ranges that extend from the Los Angeles basin and Transverse Ranges southward the entire length of Baja California. The eastern ranges, including the Santa Rosa Mountains are typically over high, with San Jacinto Peak reaching 10,805 feet, whereas the western ranges like the Santa Ana, Agua Tibia and Laguna mountains are lower. Like the Sierra Nevada, the Peninsular Ranges have gentle western slopes and steep eastern faces. The mountains are drained by the Santa Margarita, San Luis Rey, San Diego and San Dieguito rivers, while San Felipe Creek in the east drains into the Salton Sea. The oldest "roof" rocks in the Peninsular Ranges date to the
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
, such as limestone deposits near Riverside quarried for the concrete industry. The oldest rocks are found in the San Jacinto and Santa Rosa mountains, with
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
and
gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...
that may be up to 22,000 feet thick. With the exception of some metasedimentary and metavolcanic rocks, most rocks in the Peninsular Ranges are igneous and
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
in age, dating to the time of the
Nevadan orogeny The Nevadan orogeny occurred along the western margin of North America during the Middle Jurassic to Early Cretaceous time which is approximately from 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different kin ...
. Most intrusive igneous rocks are tonalite, granodiorite, quartz diorite or gabbro. Geologists group the plutons of the Peninsular Ranges as the Southern California batholith, which includes several large individual plutons like the San Marcos Gabbro, Woodson Mountain Granodiorite or Bonsall Tonalite. Compared with the Sierra Nevada, rocks from this time period tend be more calcic than silicic. The rocks likely formed much further away from the Sierras and were relocated by the dramatic movements of faults. A thick sequence of mostly terrestrial sedimentary rocks including the Rosario, Ladd, Trabuco and Williams formations is exposed on the western slope of the Santa Ana Mountains and Santa Ana Canyon, stretching southward to Camp Pendleton, San Onofre, and smaller exposures in Encinitas, Leucadia, Point Loma and La Jolla. These rocks date to the Cretaceous, with a lower sequence of conglomerate overlain by sandstone and shale, with huge
ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
fossils. In the early
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
, widespread erosion of crystalline rocks inland produced huge quantities of sediment which deposited on the Cretaceous rocks of the Peninsular Ranges. Examples include the Silverado Formation with 1400 feet of
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
terrestrial sedimentary rock in the Santa Anas or the
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
Poway Formation near San Diego. The Poway Formation has rounded metavolcanic pebbles with no known source nearby, suggesting an original source somewhere in Sonora before a major offset to the north by faults. Much more recent
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58
. In the nineteenth century, mining began in the vicinity of Julian, extracting nickel and gold, in the Julian Schist. Hot springs including San Jacinto, Eden, Saboba and Gilman are active in the San Jacinto Mountains due to the presence of the San Jacinto fault zone and Elsinore was founded on its hot springs.


San Francisco Bay, San Pablo Bay and Suisun Bay

The three interconnected Suisun, San Pablo and San Francisco bays occupy a structural depression dating to the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
and include rocks in the Shoo Fly complex and Grizzly Formation. These deposited as part of a series of small island arcs, "rafted" against the coast of the proto-North American continent
Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although ...
. Based on the presence of flat-topped
guyot In marine geology, a guyot (pronounced ), also known as a tablemount, is an isolated underwater volcanic mountain ( seamount) with a flat top more than below the surface of the sea. The diameters of these flat summits can exceed .guyots, suggesting a deep-sea origin for the base of the Sierras sometime before the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
. In the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
, the Paleozoic rocks of the Calaveras complex were heaved under the Shoo Fly complex by the Sonoma orogeny, which is preserved in roof pendants and country rock inclusions. During the
Nevadan orogeny The Nevadan orogeny occurred along the western margin of North America during the Middle Jurassic to Early Cretaceous time which is approximately from 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different kin ...
in the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
, extensive folding and faulting altered the rocks and huge granite
batholiths A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, suc ...
erupted. The Foothill Metamorphic Belt likely came ashore as an island arc terrane, colliding with the edge of North America to the west of the current Melones fault zone. This added metavolcanic and metasedimentary rocks to the slowly building Sierras. Geologists debate how high the early Sierra Nevada were. Twenty-five thousand feet of Jurassic marine sediments in the Sacramento Valley do not necessarily correspond exactly to the height of the mountains, but fist-sized cobbles in conglomerates from the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
suggest steep conditions and potentially higher altitudes than today. Most erosion of the Sierra Nevada was finished by the
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
and faulting may have reactivated the roots of the mountains to create the current mountain range. The geomorphology of the Sierra Nevada is comparatively recent, dating to as recently as the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
. Movement along the Sierra Nevada fault helped to create the new Muir Crest and parts of the mountain range rose up to 10,000 feet over the last three million years, creating a steep face to the west of Owens Valley. North of the San Joaquin River, the mountains have a tilted-block pattern caused the Sierra Nevada fault, which is interpreted as being similar to the more common
Basin and Range Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...
terrain to the east. However, the Greenhorn Fault system is more active to the south, extending to the Tehachapi Mountains and causing more plateau-like landforms. Volcanic eruptions in the
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
between 9.5 and 3.5 million years ago filled old eroded canyons in parts of the Sierras with lava flows. The
Kern River The Kern River, previously Rio de San Felipe, later La Porciuncula, is an Endangered, Wild and Scenic river in the U.S. state of California, approximately long. It drains an area of the southern Sierra Nevada mountains northeast of Bakersfiel ...
and
San Joaquin River The San Joaquin River (; es, Río San Joaquín) is the longest river of Central California. The long river starts in the high Sierra Nevada, and flows through the rich agricultural region of the northern San Joaquin Valley before reaching Suis ...
both run in valleys "refilled" with lava. Rhyolite volcanic ash buried other streams during the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
forming
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
that early miners need to dig through to get at placer gold, and many old buildings in the region are made of blocks of tuff.


Transverse Ranges

The
Transverse Ranges The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie within Santa B ...
extend from Point Arguello to
Joshua Tree National Park Joshua Tree National Park is an American national park in southeastern California, east of San Bernardino and Los Angeles and north of Palm Springs, California, Palm Springs. It is named after the Joshua trees (''Yucca brevifolia'') native to t ...
, bounded by the San Andreas Fault to the north. It is the only coastal mountain range in the US—and potentially North America—with rocks older than the
Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...
. The
Santa Ynez Mountains The Santa Ynez Mountains are a portion of the Transverse Ranges, part of the Pacific Coast Ranges of the west coast of North America. It is the westernmost range in the Transverse Ranges. The range is a large fault block of Cenozoic age created ...
extend up the coast of
Santa Barbara County Santa Barbara County, California, officially the County of Santa Barbara, is located in Southern California. As of the 2020 census, the population was 448,229. The county seat is Santa Barbara, and the largest city is Santa Maria. Santa Barba ...
and contain Franciscan basement rocks (also referred to as the Franciscan basement complex) like the Coast Ranges. These are
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
age greywacke, chert, basalt, ultrabasic rocks and
serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''ser ...
from modified oceanic crust. Subsequently, sandstone and shale deposited while the region was still underwater. Up to 10,000 feet of sandstone and red shale deposited during the
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
, after which sea levels dropped in the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
preserved the sand, gravel and silt of the Sespe Formation. Before the end of the Oligocene, sea levels rose again leaving behind the Vaqueros Formation and then the
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
deep water silt and clay of the Rincon Formation. As deep basins up to one mile deep formed in the Miocene and filled with thick sediments, volcanic eruptions related to the San Andreas Fault led to rhyolite and basalt eruptions. All of these rocks were uplifted in the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
at the same time as the Coast Range orogeny, formed an anticlinal arch or tilted block against the Santa Ynez fault in the north. Because the mountain range is young only a very narrow coastal plain has developed around Santa Barbara. Similar rock formations and patterns are found throughout Ventura County, in the Topatopa Mountains and Pine Mountains. Thick
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Santa Monica Mountains The Santa Monica Mountains is a coastal mountain range in Southern California, next to the Pacific Ocean. It is part of the Transverse Ranges. Because of its proximity to densely populated regions, it is one of the most visited natural areas in ...
and the Channel Islands are different than the mountains to the north because they have granitic and metamorphic basement rocks more like the Sierra Nevada. The oldest rock in this part of the range is the Santa Monica Slate. Thick sequences of marine rocks from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
through the
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
and
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
are common in the mountains and on San Miguel Island. During the Miocene, a deep marine channel filled with up to 15,000 feet of sediment which is most of the rock exposed on the Channel Islands. Pillow structures from rapid cooling water indicate underwater volcanism that produced basalt, andesite and diabase flows during the Miocene. In fact volcanic rocks are 10,000 feet thick in the western part of the Santa Monica Mountains. The San Onofre Breccia also formed during this period with distinct
glaucophane Glaucophane is the name of a mineral and a mineral group belonging to the sodic amphibole supergroup of the double chain inosilicates, with the chemical formula â˜Na2(Mg3Al2)Si8O22(OH)2. Glaucophane crystallizes in the monoclinic system. Name G ...
schist, gabbro, limestone and greenschist. The Transverse Ranges are poorly drained by streams, but subject to periodic intense flooding, typically every 20 to 25 years. In 1815, the Los Angeles River, which then drained to Long Beach, flooded so substantially that it changed course, joining Ballona Creek and flowing to Santa Monica Bay, before another flood in 1825 redirected it back to Long Beach. Serious flooding in 1862 created a three mile wide lake in the Santa Ana River, while serious flooding in 1938 inundated the San Fernando Valley and parts of the Los Angeles coastal plain, damaging 100 bridges and killing 43 people.


Natural resource geology


Gold mining in the Sierra Nevada

Most of the gold historically mined in California originated in the Mother Lode belt, located in the foothills of the western Sierras. Most of the gold deposits date to the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
and formed in narrow belt around the Melones fault in quartz veins. Deep hydrothermal systems active in marine sedimentary rocks as they were being metamorphosed emplaced the gold. Initially, hydraulic mining was used to get at placer deposits, but it destroyed the landscape and choked rivers with sediments, ultimately being banned the California government in 1884.


Mining in the Klamath Mountains

Historically, 20 percent of the four million ounces of gold mined in California originated in the Klamath Mountains. Major Pierson Reading found gold in 1848 in the Trinity River near Douglas City. Miners extracted placer gold or dug up fossil placers in the Weaverville Formation and Hornbrook Formation. Gold lodes upstream of the placers were found as well, the largest being French Gulch 15 miles west of Redding. Gold appears in quartz veins that cut through slate, siltstone and shale originating in the Shasta Bally batholith. In addition to gold, platinum is sometimes found with gold placers. Chromite weathers out of peridotite in the Josephine ophiolite in Del Norte County and some beach placers close to Crescent City have up to seven percent chromite. The West Shasta district has a long history of copper and zinc production out of chalcopyrite and sphalerite. These sulfide minerals derive from the Copley Greenstone and or sea floor vents when the region was far offshore and formed as hot water "invaded" the Balaklala rhyolite. Around Shasta Reservoir are other copper and zinc deposits in the Triassic-age Bully Hill rhyolite.


Mercury and gold mining in the Coast Ranges

About 85 percent of mercury produced in the US throughout its history was mined in the Coast Ranges, with about $200 million worth extracted between 1850 and 1980. Mercury was first discovered in Santa Barbara County in 1796. New Idria, New Almaden and mines in the Mayacmas Mountains have been the main sources throughout history. The New Almaden mine opened in 1824, ultimately extending 2,450 feet below ground. By 1861 it already extended 250 feet below ground and produced 970 flasks of mercury a month. In the late 20th century, enough gold was found in association with the mercury, arsenic, tungsten and thallium to open the McLaughlin mine in the Mayacmas Mountains around Knoxville.


Oil and gas in California

Over 40 different oil and gas fields are found in association with the Transverse Ranges and their surrounding basins. Oil was first extracted in 1850 from the Pico Canyon field, close to Newhall with larger-scale production by 1875. The Ventura Avenue field, north of Ventura is one of the largest fields in California, producing since 1903. The small Conejo field to the east of Camarillo was geologically unusual in that the reservoir rock is fractured volcanic rock from the Miocene. Its main production ran from 1892 to the 1940s, supplying lubricating oil for other refineries. A machinist leased the property and used windmills to get small remaining amounts of oil out. California was the first place in the US to develop offshore oil drilling in the Summerland field, first found in 1896. In all, 20 oil fields are located in the Santa Barbara Channel, with one of the largest—the Dos Cuadras field—found in 1968, although a major spill on January 18, 1969, hampered interest in the field. Depth to oil is very shallow in the Santa Barbara Channel fields, at only 300 feet below the sea floor. Oil drilling in the Wilmington field cause up to 30 feet of subsidence at the eastern end of Terminal Island between 1937 and 1958. Construction workers needed to build dikes to protect a power plant and jack up bridges. Oil is also abundant in the San Joaquin Valley, but almost non-existent in the Sacramento Valley. Gas was first consumed in Stockton in the 1850s and the massive Rio Vista gas field was discovered in 1936. Substantially folding at the edge of the valley creates famous oil producing dome structures like Lost Hills and Kettleman Hills.


References

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California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...