Named as uppermost of two members of upper part of Fort Union Formation for Shotgun Butte, Fremont Co, WY, Wind River basin; type section at Shotgun Butte, secs 21, 26-28, T6N, R1E. Outcrop extends southward for 6 mi from Shotgun Butte toward Little Dome anticline; also exposed at Twin Buttes, 8 mi east of Shotgun Butte. Unit is widespread in subsurface of Wind River Basin. Locally, unit forms ledges; outcrops mostly deeply weathered and dissected. Consists of even-bedded soft claystone, siltstone, shale and sandstone; locally contains conglomerate in upper part. Unit is mostly gray, olive-drab, brown, buff and tan; a few zones are pale-red and purple. Sandstone is mainly fine grained, nonresistant and porous. Thickness at type is 2830 ft; 1265 ft at Twin Buttes and 1190 ft at Armstrong Mine (near Little Dome anticline). At type section detailed descriptions not obtained as many intervals covered by slope wash. At outcrops unit conformably overlies unnamed lower part of Fort Union; contact with overlying Indian Meadows Formation is conformable in places and elsewhere is an angular unconformity. In subsurface, unit overlies and interfingers with Waltman Shale Member (new) of Fort Union. Measured sections. Cross sections. Vertebrate fossil list. Electric log characteristics. Deposited in marginal marine environment. Middle Paleocene or early late Paleocene (Torrejon or early Tiffany) to possibly earliest Eocene age.

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