The Riverside Mountains are a mountain range in

Riverside County Riverside County is a county located in the southern portion of the U.S. state of California. As of the 2020 census, its population was 2,418,185, making it the fourth-most populous county in California and the 10th-most populous in the Unit ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. The town of

Vidal, California Vidal, California is a small unincorporated community located in San Bernardino County, California on U.S. Route 95, north of Blythe, California, United States and south of Needles. The town is west of the townsite of Earp, California and ...

is located in the West Riverside Mountains.

Geography

The Riverside Mountains are in the

Colorado Desert The Colorado Desert is a part of the larger Sonoran Desert located in California, United States, and Baja California, Mexico. It encompasses approximately , including the heavily irrigated Coachella, Imperial and Mexicali valleys. It is home to ...

, in the

Lower Colorado River Valley The Lower Colorado River Valley (LCRV) is the river region of the lower Colorado River of the southwestern United States in North America that rises in the Rocky Mountains and has its outlet at the Colorado River Delta in the northern Gulf of ...

region. They are southeast of the Turtle Mountains and north of the

Big Maria Mountains The Big Maria Mountains are located in the southeastern part of the U.S. state of California, near the Colorado River and Arizona. The range lies between Blythe and Vidal, and west of U.S. Route 95 in California and east of Midland. The mounta ...

, and the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

borders its eastern perimeter. The high point of the range is .

Riverside Mountains Wilderness

The Riverside Mountains Wilderness was established in 1994 and is managed by the

Bureau of Land Management The Bureau of Land Management (BLM) is an agency within the United States Department of the Interior responsible for administering federal lands, U.S. federal lands. Headquartered in Washington, D.C., the BLM oversees more than of land, or one ...

. The Colorado River parallels this 24,004 acre wilderness on its eastern edge. The landscape varies from gently sloping bajadas to steep, rugged interiors. Washes emerging from canyons divide the bajadas below. Numerous peaks in the Riverside Mountains give this small range a rough, craggy appearance. Two sensitive plant species, the foxtail cactus and California

barrel cactus Barrel cacti are various members of the two genera '' Echinocactus'' and '' Ferocactus'', endemic to the deserts of Southwestern North America southward to north central Mexico. Some of the largest specimens are found in the Sonoran Desert. Des ...

; and a small herd of Burro deer (''Odocoileus hemionus eremicus'') live in the Riverside range.Riverside Mountains Wilderness
- BLM

Geology

Maria Fold and Thrust Belt

The Riverside Mountains are one of several ranges that constitute the Maria Fold and Thrust Belt (MFTB). The Maria Fold and Thrust Belt underwent generally thick-skinned (involving

basement rocks In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

) north–south-trending crustal shortening in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. The structures of the MFTB are exposed by to later generally east–west-trending large-scale crustal extension in the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

, through what is known to geologists as the Colorado River Extensional Corridor. This north–south shortening is anomalous, as crustal shortening in the rest of the

North American Cordillera The North American Cordillera, sometimes also called the Western Cordillera of North America, the Western Cordillera, or the Pacific Cordillera, is the North American portion of the American Cordillera, the mountain chain system along the Pacifi ...

is oriented generally east–west because of the generally east–west compression that was due to the subduction of the Farallon plate under western North America. Also unlike the rest of the North American Cordillera, deformation in the Maria Fold and Thrust Belt involved rocks of the

North American Craton North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north'' ...

, most notably the Grand Canyon sequence of sedimentary rocks.

Rocks

The Riverside Mountains contain rocks from both the lower and upper plates of a large

detachment fault A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade me ...

and

metamorphic core complex Metamorphic core complexes are exposed areas of deep Crust (geology), crust brought to the surface by crustal extension (stretching). They form, and are exhumed, through relatively fast transport of middle and lower continental crust to the Earth's ...

system as a result of the

-age extension. The lower plate consists of a stack of metamorphosed units, which comprise

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 143.1 Mya. ...

metavolcanic Metavolcanic rock is volcanic rock that shows signs of having experienced metamorphism. In other words, the rock was originally produced by a volcano, either as lava or tephra. The rock was then subjected to high pressure, high temperature or both ...

s, the metamorphosed Grand Canyon sequence, the metamorphosed

McCoy Mountains The McCoy Mountains are located in southeastern California in the United States. The southeast terminus of the range lies adjacent the western edge of the Parker Valley in a southern stretch of the Lower Colorado River Valley corridor. Geography ...

Formation and related

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

rocks, and the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, 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 t ...

basement. The upper plate of the detachment fault consists of a small

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

containing

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

-age syntectonic (deposited during tectonic activity) volcanic units, conglomerates, and other

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

References

External links

Riverside Mountains Wilderness
- Wilderness Connect
Shaded Relief map: Whipple, Turtle, Big Maria, and Riverside Mountains
{{authority control Mountain ranges of the Colorado Desert Protected areas of the Colorado Desert Mountain ranges of Riverside County, California Mountain ranges of the Lower Colorado River Valley Wilderness areas within the Lower Colorado River Valley Bureau of Land Management areas in California Protected areas of Riverside County, California