USGS Geoscience Data Catalog
Trumbull, J., 1960, Coal Fields of the United States (sheet 1): U.S. Geological Survey map, Scale 1:5,000,000. Tully, J., 1996, Coal Fields of the Conterminous United States: U.S. Geological Survey Open File Report 96-92, Scale 1:5,000,000.