# Chalk Butte Formation

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The **Chalk Butte Formation** is a [geologic formation](/source/Formation_(geology)) in [Oregon](/source/Oregon), which forms a part of the Idaho Group.[1] It preserves [fossils](/source/Fossils) dating back to the [Neogene](/source/Neogene) [period](/source/Period_(geology)).[2] It was proposed along with the Grassy Mountain Basalt Formation and the Kern Basin Formation as a division of the Idaho Group rocks in the Mitchell Butte Quadrangle.[3] The predominant rock types are [tuffaceous](/source/Tuffaceous) [sandstones](/source/Sandstone), [siltstones](/source/Siltstone), and [conglomerates](/source/Conglomerate_(geology)) with smaller amounts of tuff, ash beds, and freshwater [limestone](/source/Limestone).[3] A partial section at the type location determined the formation to be about 538 feet thick.[3]

## Fossil content

The following fossils have been reported from the formation:[2][4]

- *[Antecalomys valensis](/source/Antecalomys)*
- *[Basirepomys pliocenicus](/source/Basirepomys)*
- *[Copemys cf. esmeraldensis](/source/Copemys)*
- *[Cupidinimus magnus](/source/Cupidinimus)*
- *[Diprionomys parvus](/source/Diprionomys)*
- *[Dipoides vallicula](/source/Dipoides)*
- *[Eucyon davisi](/source/Eucyon)*
- *[Goniodontomys disjunctus](/source/Goniodontomys)*
- *[Hypolagus vetus](/source/Hypolagus)*
- *[Peromyscus antiquus](/source/Peromyscus)*
- *[Pliohippus spectans](/source/Pliohippus)*
- *[Plionictis oregonensis](/source/Plionictis)*
- *[Scapanus proceridens](/source/Scapanus)*
- *[Dipoides sp.](/source/Dipoides)*
- *[Spermophilus sp.](/source/Spermophilus)*
- [Camelidae indet.](/source/Camelidae)
- [Perognathinae indet.](/source/Perognathinae)
- [Soricidae indet.](/source/Soricidae)
- [?Vespertilionidae indet.](/source/Vespertilionidae)

## See also

- [List of fossiliferous stratigraphic units in Oregon](/source/List_of_fossiliferous_stratigraphic_units_in_Oregon)
- [Paleontology in Oregon](/source/Paleontology_in_Oregon)

## References

1. [Chalk Butte Formation](https://ngmdb.usgs.gov/Geolex/Units/ChalkButte_4967.html) at [USGS](/source/United_States_Geological_Survey)

1. [Chalk Butte Formation](https://paleobiodb.org/classic/displayStrata?geological_group=&formation=Chalk%20Butte&group_formation_member=Chalk%20Butte) at [Fossilworks](/source/Fossilworks).org

1. Corcoran, R. E.; Doak, R. A.; Porter, P. W.; Pritchett, F. I.; Privrasky, N. C. (1962). ["Geology of the Mitchell Butte Quadrangle, Oregon"](https://pubs.oregon.gov/dogami/gms/GMS-002.pdf). *Geological Map Series*. Portland, Oregon: State of Oregon Department of Geology and Mineral Industries. Retrieved 26 June 2024.

1. Shotwell, 1970

### Bibliography

- Shotwell, J. A (1970), "Pliocene mammals of southeast Oregon and adjacent Idaho", *[Bulletin of the Museum of Natural History, University of Oregon](/source/Bulletin_of_the_Museum_of_Natural_History,_University_of_Oregon)*. **17**: 1–103

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