The Crowder Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the Central and Western

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 ...

, in northern

Los Angeles County Los Angeles County, officially the County of Los Angeles, and sometimes abbreviated as L.A. County, is the most populous county in the United States and in the U.S. state of California, with 9,861,224 residents estimated as of 2022. It is the ...

and eastern

San Bernardino County San Bernardino County (), officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California, and is located within the Inland Empire area. As of the 2020 U.S. Census, the population was 2,181, ...

, in Southern

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 ...

. Seismo.berkeley.edu: Field Guide to the Punchbowl Fault Zone, at Devil's Punchbowl Los Angeles County Park
; San Andreas Fault Resources; University of California, Berkeley; by Frederick M. Chester; January 1999. Areas where it is exposed include at the bases of the northern

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 ...

and northwestern

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 � ...

, and in the

Cajon Pass Cajon Pass (; Spanish: ''Puerto del Cajón'' or ''Paso del Cajón'') is a mountain pass between the San Bernardino Mountains to the east and the San Gabriel Mountains to the west in Southern California. Created by the movements of the San Andreas ...

between them.San Bernardino County Museum: "Miocene Faunas in the Lower Crowder Formation"
by R.E. Reynolds, 1984.Caltech Thesis: "Neotectonics of the north frontal fault system of the San Bernardino Mountains, southern California : Cajon Pass to Lucerne Valley"
Meisling, Kristian Erik (1984), Dissertation (Ph.D.), California Institute of Technology.

Geology

The Crowder Formation was formed during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

of the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. The formation was deposited by drainages carrying distinctive volcanic and metamorphic clasts from the Victorville area southward. It overlies the crystalline San Gabriel Basement Complex in its eastern section, and the

San Francisquito Formation The San Francisquito Formation is a geologic formation located in northern Los Angeles County, California.

in its western section in the

Antelope Valley The Antelope Valley is located in northern Los Angeles County, California, and the southeast portion of Kern County, California, and constitutes the western tip of the Mojave Desert. It is situated between the Tehachapi, Sierra Pelona, and the ...

/San Gabriels.

Fossils

The formation preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

of insects, reptiles, rodents, birds, and larger mammals. The species date back to 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 ...

and Pliocene epochs of the Neogene period. 29

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

were collected by the San Bernardino County Museum from the Cajon Pass area of the Crowder Formation.

References

*"The Physical and Magnetic Stratigraphy of the Miocene Crowder Formation, Cajon Pass, Southern California"; by Douglas Scott Winston, University of Southern California; Los Angeles, 1985. Miocene California Pliocene California Miocene geology Pliocene geology Geology of Los Angeles County, California Geology of San Bernardino County, California Natural history of the Mojave Desert Antelope Valley San Bernardino Mountains San Gabriel Mountains Miocene Series of North America Pliocene Series of North America Geologic formations of California {{Neogene-stub

Geology

Fossils

See also

References