The Plush Ranch 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

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 San ...

of southern

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 ...

. 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 ...

dating back to the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/ Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stag ...

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was p ...

(

Arikareean The Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years BP, a period of . It is usual ...

in the NALMA classification).

Description

The formation is the oldest non-marine unit of the Tejon region where the small Plush Ranch Basin is formed by the bounding Big Pine/Lockwood Valley and

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...

s. The unit is composed of

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Al ...

and

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

conglomerates,

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

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 wh ...

s, and

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

s. Interbedded basalt has been dated by whole-rock and

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

K-Ar methods as ca. 26–23 Ma. Northwest of Plush Ranch Basin, on the opposite side of Mount Pinos (which includes exposures of Pelona Schist), Oligocene–Miocene strata are generally mapped as

Simmler Formation Simmler is a surname. Notable people with the surname include: * Josias Simmler (Josiah Simler, Simlerus; 1530–1576), Swiss theologian and classicist * Józef Simmler (1823–1868), Polish painter * Wilhelm Simmler Wilhelm Carl Melchior Simmle ...

, but are considered equivalent to the Plush Ranch Formation. These strata coarsen upward, from mostly sandstone at the base to coarse conglomerate at the top.Coffey et al., 2019, p.480 The lacustrine deposits represent the central and eastern parts of the Plush Ranch basin, which received little coarse siliciclastic sediment. Chironomid flies, disarticulated fish, and

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...

s indicate a more or less permanent lake.Old Frazier Borax Mine
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org Atop the Plush Ranch Formation, separated by an angular unconformity, there is the non-marine

Caliente Formation The Caliente Formation is a geologic formation in California. It preserves fossils dating back to the Neogene period. See also * List of fossiliferous stratigraphic units in California This article contains a list of fossil-bearing stratig ...

, comprising fluvial and lacustrine conglomerate, sandstone, and mudstone, with minor

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 ...

aceous and limestone beds.

Fossil content

The following fossils have been reported from the formation:Plush Ranch Formation
at

.org ;Insects *

Blattodea Blattodea is an order of insects that contains cockroaches and termites. Formerly, termites were considered a separate order, Isoptera, but genetic and molecular evidence suggests they evolved from within the cockroach lineage, cladistically m ...

Stylotermitidae Stylotermitidae is a family of termites in the order Blattodea. There are two extinct and one extant genera in Stylotermitidae, with more than 50 described species. Genera These three genera belong to the family Stylotermitidae: * '' Stylotermes ...

*** '' Parastylotermes frazieri''Snyder, 1955

References

Bibliography

* * {{cite journal , last=Snyder , first=T. E , year=1955 , title=A new fossil termite, ''Parastylotermes frazieri'', from California (Isoptera, Rhinotermitidae) , journal=

Proceedings of the Entomological Society of Washington ''Proceedings of the Entomological Society of Washington'' is a peer-reviewed scientific journal of entomology published by the Entomological Society of Washington. The journal was established in 1886 and is currently published four times per year ...

, volume=57 , pages=79–80 Geologic formations of California Miocene Series of North America Miocene California Oligocene Series of North America Paleogene California Chattian Stage Aquitanian (stage) Arikareean Sandstone formations of the United States Shale formations of the United States Siltstone formations Oligocene volcanism Alluvial deposits Lacustrine deposits Paleontology in California