Named as a formation in Hay Creek coal field, Crook Co, WY in Powder River basin, presumably for exposures along the south fork of Hay Creek, Crook Co, WY. Type section not designated. Formerly included in Dakota group of Newton and Jenney (1880). Consists of (descending): massive sandstone, ochre-yellow, weathering yellowish-brown on the surface, underlain by gray and drab clay shales with local thin coals and plant remains, 10-20 ft; coal, mined at the mines of Larrabee and Young and at Barrett, 2-6 ft; gray clay shales and sandy shales with plant remains, 20-35 ft; soft gray or yellow sandstones with carbonized plant remains, 5-20 ft. Overlain by Barrett shale (new) without positive evidence of unconformity; unconformably overlies Beulah clay (new). Early Cretaceous in age, based on plant remains [reported by Fontaine, W. M., 1899, Notes on Lower Cretaceous plants from the Hay Creek coal field, Crook County, Wyoming: U.S. Geological Survey 19th Annual Report, pt. 2, p. 645-702].

Source: GNU records (USGS DDS-6; Denver GNULEX).

Name not used in the area of the Hay Creek coal field, Crook Co, WY. Lakota formation used to include rocks at about the same stratigraphic position. Is Early Cretaceous in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).