Luppens, J.A., Scott, D.C., Haacke, J.E., Osmonson, L.M., Rohrbacher, T.J., and Ellis, M.S., 2008, Assessment of Coal Geology, Resources, and Reserves in the Gillette Coalfield, Powder River Basin, Wyoming: U.S. Geological Survey Open-File Report 2008-1202.
http://pubs.usgs.gov/of/2008/1202/
Status Report: USGS Coal Assessment of the Powder River Basin, Wyoming (Gillette coalfield, Sheridan-Birney coalfields, Birney-Custer-Recluse coalfields): USGS Open-File Report 2006-1072.
Coal assessment regions of the United States.