The entire surface of Audubon County is covered with a thick deposit of glacial drift, loess, etc. Erosion has not been great enough in any part of the county to expose indurated rock. Two glacial stages are represented in the drift deposits - the Nebraskan and Kansan. Loveland and Peorian loesses overlie the drift. The Nebraskan is the thicker of the drift deposits. Several wells have been drilled to or through basal Nebraskan sand, and thicknesses of Nebraskan drift of 2SO to 3SO feet are not uncommon. The top of the Nebraskan can be easily determined where the Nebraskan gumbotil outcrops. The outcrops of Nebraskan gumbotil are numerous in nearly all parts of Audubon County. The average thickness of Kansan drift is SS to 60 feet. A thin deposit of Loveland loess overlies the Kansan gumbotil in places. Nearly the whole land surface is mantled with a deposit of Peorian loess ranging in thickness from a few inches to 30 or more feet. In preparing the detailed Pleistocene map of the county, the contact between Nebraskan and Kansan deposits was drawn on the basis of the Nebraskan gumbotil outcrops and the relationship of the Nebraskan gumbotil level to the present topography.
Proceedings of the Iowa Academy of Science
©1939 Iowa Academy of Science, Inc.
Yoho, W. Herbert
"The Pleistocene Geology of Audubon Country, Iowa,"
Proceedings of the Iowa Academy of Science, 46(1), 249-249.
Available at: https://scholarworks.uni.edu/pias/vol46/iss1/58