Calhoun County is located in northwestern Iowa in the fourth tier of counties south of Minnesota and in the fourth tier east of the Missouri River. It is all in the Wisconsin drift soil area and hence the soils are all of glacial origin.
Brown, P. E.; Benton, T. H.; Leighty, W. J.; and Meldrum, H. R., "Soil Survey of Iowa, Report No. 72—Calhoun County Soils" (1933). Soil Survey Reports. 80.