Geology of the Driftless Area

ABSTRACT The Driftless Area is a region of roughly 22,000 km2 almost entirely in southwestern Wisconsin and adjacent northwestern Illinois that contains no evidence for glaciation during the Quaternary. Both in terms of topography and geomorphic process, it stands in stark contrast to the surrounding glaciated landscapes of the Midwestern United States. The nearly flat-lying Paleozoic sedimentary rocks in the region are deeply incised by the dendritic drainage system of the upper Mississippi and lower Wisconsin Rivers and numerous of their tributaries. Records of geologic processes that predate the Quaternary glaciations are exposed at the near-surface. The landscape is blanketed by loess of the Kieler Formation and was affected by mass wasting and a range of periglacial processes that were pervasive during permafrost conditions that existed between 33 and 14 ka. Post-glacial fluvial systems preserve myriad examples of channel adjustment to changes in sediment supply from the transition of glacial to interglacial conditions, changes in discharge across periods of Holocene climate change, and responses to Euro-American settlement of the landscape.