1. Energy resources map of the Powder River Basin, Wyoming and Montana [cartographic material] Yale Public content 1973. 2013-05-22T17:40:03Z. 2013-06-13T15:35:43Z. Keefer, William Richard, 1924-. Dept. of the Interior, U.S. Geological Survey. English. Public. Powder River Basin (Wyo. and Mont.).