1. Geologic map of the frontal fold and thrust zone in the Blacktail Mountains, Beaverhead County, Montana [microform] Yale Public content 1987. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey : [Books and Open-file Reports Section, distributor]. English. Public. Montana and Beaverhead County.