Isolated patches of rough terrain in the unglaciated Driftless
Area, primarily in southwestern Wisconsin, stand out from the
surrounding, smoothed glaciated ground. Thoroughly dissected by
tributaries of the Mississippi River, the topography within these
"islands" was engulfed but never overridden by the ice. The appearance
of the Driftless Area landscape today probably is much like that
of adjacent glaciated landscapes
prior to the first Pleistocene ice advance.