Johnson, William D. The square buttes coal field Oliver and mercer counties North Dakota / by William D. Johnson and Robert P. Kunkel. -- Washington : United States Government Printing Office, 1959 - 90 p. + map. -- (Geological Survey Bulletin ; 1076). Subjects--Topical Terms: Dakota del NorteRocas carboníferas Universal Decimal Class. No.: 552.57(784)