1. Oil and gas investigations, map OM (series). 111. Geology of Hardin area. Pig Horn and Yellowstone Counties, Mont.; by P. W. Richards and C. P. Rogers, jr. [with text by P. W. Richards]. Scale 1 m. = 1 in. Bookmark Corporate/Agency Authors: Geophysical investigations map GP (series). Publisher: Geophysical investigations map GP (series). Date: 1951 SuDoc number: I 19.25/4:111/sh.1,2