Uinta Formation
Stratigraphic range: Eocene

Characteristic exposure of the Uinta Formation

Type| Formation
Lithology
Primary| mudstone and sandstone
Other| gilsonite
Location
Region| Utah
Country| United States
Mudstones of the Uinta Formation (Uinta "C"), Uintah County, Utah. Uinta Formation (Uinta "C"), Uintah County, Utah

The Uinta Formation is a geologic formation in northeastern Utah. The name appears on a geologic map accompanying the Clarence King Fortieth Parallel report for 1876[1] but not defined until 1878[2] as the Uinta Group. As defined, it consisted of all Tertiary strata overlying the Green River Formation and was composed of coarse, conglomeratic sandstones, passing up into finer-grained sandstones and calcareous mudstones. Numerous vertebrate fossils were collected and described by Othniel C. Marsh of Yale University. The formation was subsequently subdivided into three informal horizons (A, B, C) based on mammalian fossils.[3] Horace Wood[4] proposed the name Wagonhound Member (from Wagonhound Canyon) for Uinta A+B and Myton Member (from the town of Myton) for Uinta C. However, these names are not based on lithology, but on mammalian vertebrate faunas. For that reason, they have not been accepted as proper lithostratigraphic names.

Members of the Uinta Formation

Gilsonite, Gottonwood Dike intruded in the Uinta Formation

Today the formation is subdivided into three informal members:[5]

Member A: Yellowish-gray and yellowish-brown, fine- to very fine grained sandstone and siltstone, with minor amounts of conglomerate, shale, and tuffaceous beds. It intertongues with the underlying Parachute Creek Member of the Green River Formation. It has produced a K-Ar radiometric date 43 Ma.

Member B: Light-gray, light-greenish-gray, light-brown, and light-purple, mudstone and claystone with interbeds of greenish-gray, yellow, and brown fine-grained sandstone, and minor conglomerate and tuffaceous beds. Much of the gilsonite comes from this member in the southern part of the Uinta Basin.

Member C: Soft, light-gray, greenish-gray, white, grayish-purple, red, and pale-yellow shale, mudstone, claystone, and minor sandstone with local tuffaceous interbeds. The eroded sandstones form the strange shaped hoodooes at Fantasy Canyon.

Mammalian Biostratigraphy

Fossil mammals from the Uinta formation define the Uintan North American Land Mammal Age.[6] The index taxa include: Achaenodon, Amynodon, Diplacodon, Eobasileus, Leptotragulus, Oxyaenodon, Oromeryx, Prodaphaenus, Protitanotherium, Protoptychus, Dolichorhinus (= Sphenocoelus), Ourayia, Procynodictis, Metarhinus, Mesomeryx, Bunomeryx, Hylomeryx, and Mytonomeryx.[7] During this interval, primates decline in diversity and relative abundance, primitive perissodactyls were replaced by more advanced forms, such as the Amynododontidae, new artiodactyls appeared, including Oromerycidae, Camelidae, Agriochoeridae, and Protoceratidae. Among rodents, Cylindrodontidae and Eomyidae replaced the Ischyromydidae, and rabbits make their first appearance as the tropical and subtropical habitats began to be replaced by more open habitats.

More recent research has subdivided the Uintan into smaller intervals called biochronological zones (biochrons) based on distinctive suites of mammalian species: early (Ui1), middle (Ui2) and late (Ui3).[7][8] These biochrons are based on taxa and do not correspond to the three informal members listed above.

* Differentially cemented and eroded sandstone (member C), Fantasy Canyon

*   *   *   * Uinta C in the western part of the Uintah Basin

## See also

* List of fossiliferous stratigraphic units in Utah
* Paleontology in Utah

## References

1. ↑ King, Clarence, 1876, Geological and topographical atlas accompanying the report of the geological exploration of the Fortieth Parallel [from the Sierra Nevada to the eastern slope of the Rocky Mountains], made by authority of the Honorable Secretary of War, under the direction of Brigadier and Brevet Major General A.A. Humphreys, Chief of Engineers, USA: Washington, D.C., U.S. Geological Exploration of the Fortieth Parallel (King), 12 sheets., See also U.S. War Dept., Chief Eng. Ann. Rpt., 1876, (U.S. 44th Cong., 2nd Sess., House of Representatives Exec. Doc. 1, pt. 2, v. 2, pt. 3) App. 2, p. 217-218
2. ↑ King, Clarence, 1878, Systematic geology, IN Report of the Geological Exploration of the Fortieth Parallel made by order of the Secretary of War according to acts of Congress of March 2,1867, and March 3, 1869, under the direction of Brigadier and Brevet Major General A.A. Humphreys, Chief of Engineers, USA: Washington, D.C., U.S. Geological Exploration of the Fortieth Parallel (King), v. 1, 803 p.
3. ↑ Peterson, O. A. 1919. Report upon the Material Discovered in the Upper Eocene of the Uinta Basin by Earl Douglass in the years 1908-1909, and by 0. A. Peterson in 1912. Annuals of the Carnegie Museum, v. 12 (2-4) pp. 40-168.
4. ↑ Wood, H.E., 1934. Revision of the Hyrachyidae. Bulletin of the American Museum of Natural History v. 67, article 5, p. 181-295.
5. ↑ Spinkle, D.A., 2006, Interim geologic map of the Vernal 30' x 60' quadrangle, Uintah and Duchesne Counties, Utah, and Moffat and Rio Blanco Counties, Colorado. Utah Geological Survey Open File Report 470. https://geology.utah.gov/map-pub/publications/#
6. ↑ Wood, H. E., R. W. Chaney, J. Clark, E. H. Colbert, G.L. Jepsen, J.B. Reeside, and C. Stock. 1941. Nomenclature and correlation of the North American continental Tertiary. Geological Society of America Bulletin v. 52, pp. 1-48.
7. ↑ 7.0 7.1 Robinson, P., G. F. Gunnell, S. L. Walsh, W. C. Clyde, J. E. Storer, R. K. Stucky, D. J. Froehlich, I. Ferrusquia-Villafranca, and M. C. McKenna. 2004. Wasatchian through Duchesnean biochronology; pp. 106-155 in M. O. Woodburne (ed.), Late Cretaceous and Cenozoic Mammals of North America. Columbia University Press, New York, New York
8. ↑ Gunnell, G.F., Murphey, P.C., Stucky, R.K., Townsend, K.B., Robinson, P., Zonneveld, J.P., Bartels, W.S. and Albright, L.B., 2009. Biostratigraphy and biochronology of the latest Wasatchian, Bridgerian, and Uintan North American land mammal “ages”. Museum of Northern Arizona Bulletin 65, pp.279-330.

## Further reading

* Hayden, Martha (1994), "PALEONTOLOGY IN UTAH", Utah History Encyclopedia, University of Utah Press, ISBN 9780874804256, https://www.uen.org/utah_history_encyclopedia/p/PALEONTOLOGY.shtml, retrieved June 12, 2025

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