The Diligencia Formation (Td) 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 ...

cropping out in the

Orocopia Mountains The Orocopia Mountains are located in Riverside County in southern California, United States, east of the Coachella Valley, west of the Chuckwalla Mountains, and south of Interstate 10 in the Colorado Desert. The range lies in an east-west dir ...

in 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 ...

. It preserves mammal

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 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).Diligencia Formation
at

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Description

The non-marine Diligencia Formation, defined by Crowell in 1975, 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 ...

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

, 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, ...

s and

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. It contains interbedded

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

and

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

flows, 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. 24–21 Ma), and andesitic sills and dikes.Coffey et al., 2019, p.481Canyon Spring
at

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Fossil content

The formation has provided the following fossils: ;Mammals *

Artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poste ...

s **

Merycoidodontidae Merycoidodontoidea, sometimes called "oreodonts" or " ruminating hogs", is an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were gen ...

*** '' Merychyus cf. minimus''Woodburne & Whistler, 1973

References

Bibliography

* * {{cite LSA , last=Woodburne , first=M. O. , first2=D. P. , last2=Whistler , year=1973 , title=An Early Miocene Oreodont (Merychyinae, Mammalia) from the Orocopia Mountains, Southern California , journal=

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is published by the Paleontological Society. Indexing The ''Journal of Paleontology'' is indexed in: *BIOSIS Previews *Science Citatio ...

, volume=47 , pages=908–912 Geologic formations of California Miocene Series of North America Oligocene Series of North America Miocene California Paleogene California Chattian Stage Aquitanian (stage) Sandstone formations of the United States Conglomerate formations Shale formations of the United States Siltstone formations Oligocene volcanism Alluvial deposits Fluvial deposits Lacustrine deposits Paleontology in California Andesite formations

Description

Fossil content

See also

References

Bibliography