J. S. Pomeroy W. R. Kohl W.E. Davies 1976 <p>This map is one result of a series of studies sponsored by the Appalachian Regional Commission as part of a larger U.S. Geological Survey program of environmental analysis of a part of southwestern Pennsylvania. The map summarizes surface features resulting from coal mining. The distribution of surface features is largely from 1973, 1:12,000 scale aerial photographs verified by field reconnaissance in 1973 and 1974. Supplementary interpretations relative to surface subsidence were done using 1939 aerial photographs.</p> application/pdf 10.3133/mf685C en U.S. Geological Survey Map of coal-mining features, Allegheny County, Pennsylvania reports