Hillsides of the Driftless Area (image by McGheiver on Wikimedia) - On the ground, the topography is even more dramatic, particularly along the Mississippi River valley. In the image below, two hillsides part of Great River Bluffs State Park in Minnesota show the steepness of relief that can be found in the area.
Topography of the Driftless Area and surrounding regions - While in most parts of the Upper Midwest, the Paleozoic stratigraphy is buried under glacial deposits, millions of years of uninterrupted erosion have spectacularly dissected the landscape of the Driftless Area, creating 150+ m bluffs and narrow valleys. This dissected landscape stands out in sharp contrast to the flatter glaciated areas which surround it, as shown in the image.
Glacial advances relative to the formation of the Driftless Area (Reinertsen, 1992*) - The maps show the maximum extent of glaciers at (a) 1 million years ago, (b) ~600,000 years ago, (c) ~250,000 years ago (the Illinoian glaciation) and (d) ~22,000 years ago (Wisconsinan glaciation). In all of those reconstructions, there’s a stippled doughnut hole that defines the Driftless Area.