1. Structure, coal thickness, and overburden thickness of the Wall Coal Resource Unit, west half of the Birney 30ʹ x 60ʹ quadrangle, Big Horn and Rosebud counties, Montana Yale Public content 1987. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Map Distribution. English. Public. Montana, Big Horn County, and Rosebud County.