The Arikaree Formation, also Arikaree Group or Arikaree Sandstone is a

geological unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize ...

in the central

High Plains High Plains refers to one of two distinct land regions: *High Plains (United States), land region of the western Great Plains * High Plains (Australia), land region adjacent to the Great Dividing Range See also * Altiplano (disambiguation) The ...

of the western United States. It 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 to the late

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...

to early

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 recent" ...

References

Neogene geology of South Dakota Neogene Montana Paleogene geology of North Dakota Neogene geology of Wyoming {{Paleogene-stub