1. Structure-contour maps of the Powder River basin, Montana and Wyoming Yale Public content 1996. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by U.S.G.S. Information Services. English. Public. Powder River Watershed (Wyo. and Mont.). Cretaceous, Jurassic, Pennsylvanian, Permian, and Triassic.