The landscape of the Upper Midwest and Great Lakes region demonstrates the effects of Pleistocene glaciation: flattened terrain, glacial lakes and till enriched soil. But one area, in southwest Wisconsin defies this description; spilling into southeast Minnesota, northeast Iowa and extreme northwest Illinois, this swath is characterized by a heavily dissected plateau of ridges and valleys.
Known as the Driftless Area and often called the Paleozoic Plateau, this terrain escaped the last two glaciations of the Pleistocene, preserving its topography and keeping its soil devoid of glacial drift. The last glacier, the Wisconsin (70,000 to 10,000 years ago), was diverted by the resistant Baraboo Ridge, north of the Driftless Area and the ice moved to the east and west of the plateau, merging to its south. Surrounded by ice near the end of the Epoch, the area was spared glaciation as the climate warmed and the ice sheets retreated into Canada before spreading inward.
Like the Ozarks of Missouri-Arkansas, this plateau is composed primarily of early Paleozoic limestone, dolomite and sandstone, yielding karst features (caves, springs, sinkholes) throughout the region. The Upper Mississippi cuts through the western portion of the Plateau and its many tributaries, augmented by glacial meltwater, molded the rugged, scenic landscape that we find today.