Botanically and geologically, one of the most interesting areas in the Upper Middle West is the "Driftless Area." Covering 15,000 square miles of southwestern Wisconsin and adjacent Illinois, Iowa and Minnesota, this area is about twice the size of the state of New Jersey. With the exception of certain marginal areas such as northeastern Iowa, the "Driftless Area" was apparently not covered by a continental glacier during the periodic glaciation of the Pleistocene epoch. These marginal areas are believed to have been glaciated during the earliest of these periods, the Nebraskan, and most of that resulting drift has been lost through weathering and erosion.
Proceedings of the Iowa Academy of Science
©1957 Iowa Academy of Science, Inc.
Hartley, Thomas G.
"A Comparison of the Floras of Southwestern Wisconsin and Northeastern Iowa,"
Proceedings of the Iowa Academy of Science, 64(1), 199-204.
Available at: https://scholarworks.uni.edu/pias/vol64/iss1/24