 area = 2500000 sqkm John P. Bluemle; Guide to the Geology of South-Central North Dakota; Burleigh, Dickey, Emmons, Kidder, LaMoure, Logan, McIntosh, and Stutsman Counties; Educational Series 6; North Dakota Geological Survey, E. A. Noble, State Geologist; Bismarck, North Dakota; revised 1975