Cowboy Spring Formation
Stratigraphic range: late Cretaceous PreꞒ Ꞓ O S D C P T J K Pg N
Type	Formation
Underlies	Timberlake Formation
Overlies	Mojado Formation
Thickness	Over 1,000 feet (300 m)
Lithology
Primary	Limestone conglomerate
Other	Sandstone, shale, claystone, tuff
Location
Coordinates	31°36′31″N 108°38′10″W / 31.6085°N 108.6362°W / 31.6085; -108.6362
Region	New Mexico
Country	United States
Type section
Named for	Cowboy Spring
Named by	Zeller and Alper
Year defined	1965
Cowboy Spring Formation (the United States) Show map of the United States Cowboy Spring Formation (New Mexico) Show map of New Mexico

The Cowboy Spring Formation is a geologic formation in southwestern New Mexico and southeastern Arizona. It preserves fossils dating back to the late Cretaceous period.^[1][2]

The formation is primarily limestone cobble conglomerate. The massive conglomerate beds are separated by thinner beds of sandstone, shale, claystone, and tuff. The clasts in the conglomerate are of Cretaceous age and contain the foraminiferan Orbitolina and other common Cretaceous fossils. These are embedded in a red arkosic matrix. The sandstones are also mostly red and arkosic and the shale is mostly bright red. The formation interfingers with the underlying Mojado Formation, is overlain with angular unconformity by the Timberlake Formation, and has a total thickness of at least 1,000 feet (300 m).^[1]

A single latite tuff bed some 20 feet (6.1 m) is exposed in the formation.^[1]

The formation was deposited in the Little Hat Top basin, which was produced by Laramide deformation on the southwest flank of the Hidalgo uplift.^[3]

The formation was first named by Zeller and Alper in 1965 for a single outcrop in the Animas Mountains.^[1] By 1970, it had been traced into southeastern Arizona^[2] Elston and Erb recommended merging the formation with the overlying Timberlake Formation due to lack of a clear lithological distinction,^[4] but this has not been universally accepted.^[5]

• Elston, W.E.; Erb, E.E. (1977). "Cenozoic volcano-tectonic setting of KCM #1 Forest Federal Well, Animas Mountains, Hidalgo County, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Circular. 152: 53–62. Retrieved 15 September 2020.
• Hayes, P.T. (1970). "Cretaceous paleogeography of southeastern Arizona and adjacent areas". U.S. Geological Survey Professional Paper. Professional Paper. 658-B: B1–B42. doi:10.3133/pp658B.
• Seager, William (2004). "Laramide (late Cretaceous-Eocene) tectonics of southwestern New Mexico". In Mack, G.H.; Giles, K.A. (eds.). The geology of New Mexico. A geologic history: New Mexico Geological Society Special Volume 11. pp. 183–202. ISBN 9781585460106.
• Zeller, R.A. Jr.; Alper, A.M. (1965). "Geology of the Walnut Wells quadrangle, Hidalgo County, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Bulletin. 84. Retrieved 15 September 2020.