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, the population was 2,418,185, making it the fourth-most populous county in California and the 10th-most populous in the Uni ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. The town of

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

is located in the

West Riverside Mountains The West Riverside Mountains are a mountain range in Riverside County, California. References See also *Riverside Mountains *Parker Valley The Parker Valley is located along the Lower Colorado River within the Lower Colorado River Valley ...

Geography

The Riverside Mountains are in the Colorado Desert, in the Lower Colorado River Valley 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 mountains ...

, and the

Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. s ...

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 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 in So ...

; 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) north–south-trending crustal shortening in 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 ...

. 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 Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

. This north–south shortening is anomalous, as crustal shortening in the rest of the North American Cordillera is oriented generally east–west because of the generally east–west compression that was due to the subduction of the

Farallon plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...

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'' is ...

, 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 exposures of deep crust exhumed in association with largely amagmatic extension. They form, and are exhumed, through relatively fast transport of middle and lower continental crust to the Earth's surface. During th ...

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 geologic period and 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 Jurassic constitutes the middle period of ...

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 ( ), 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 Cretace ...

rocks, and the Precambrian 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 subside ...

containing

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

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

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

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