Named [informally?] for prominent hill just west of Sheep Creek canyon, south-central Owyhee Co, ID. No type locality designated. Unit previously called rhyolite of Sheep Creek in unpublished thesis (Bernt, J., 1982, Univ of ID). Exposed in Sheep Creek canyon, 1.2-4.5 km north of ID-NV border. Rhyolite is typically reddish brown, massive, lithoidal welded tuff with abundant phenocrysts; a black vitrophyre is present along southeast margin of unit. Unit is more than 170 m thick. Interpreted as a single ash flow due to a lack of internal flow structures, occurrence of deformed glass fragments and shards?, flattened pumice fragments and possible base surge deposits. Unit is probably an intracaldera facies of a more extensive ash-flow sheet. Overlies Bieroth volcanics (redescribed); underlies Whiskey Draw rhyolite (new), lapilli tuff of Sheep Creek, Johnstons Camp rhyolite (new), Cougar Point Tuff and Banbury Basalt. Geologic map. Chemical analysis. Miocene? age.

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