6 mi. to 1 in. (W 92°52ʹ--W 86°45ʹ/N 47°07ʹ--N 44°30ʹ). "Based on the work of the Soils and Geological Divisions of the Wisconsin Geological and Natural History Survey in cooperation with the College of Agriculture and the Bureau of Soils of the United States Department of Agriculture, which has been published in previous maps and reports."
Whitson, A. R.
Thompson, Carl; Dunnewald, Theodore J., 1885-1974; Wisconsin Geological and Natural History Survey.
University of Minnesota Libraries, John R. Borchert Map Library.