Driftless Area
Relief map showing primarily the Minnesota
part of the Driftless Area. The wide diagonal
river is the Upper Mississippi River. In this
area, it forms the boundary between Min-
nesota and Wisconsin. The rivers entering
the Mississippi are, from the bottom up, the
Upper Iowa, Root and Cannon Rivers. A small
portion of the upper reaches of the Turkey
River are visible west of the Upper Iowa. To
the west, outside the Driftless Area where
more regular topography is evident, tributar-
ies of the Wapsipinicon and the Cedar Rivers
are seen.
The Driftless Area or Paleozoic Plateau is
a region in the American Midwest noted
mainly for its deeply carved river valleys.
While primarily in southwest Wisconsin, it in-
cludes areas of southeast Minnesota, north-
east Iowa and northwest Illinois (see map at
right). This region includes elevations ran-
ging from 603 to 1,719 feet (184 to 524 m)
and covers an area of 16,203 square miles
(41,986 km²). This region’s peculiar terrain is
due to its having escaped glaciation in the
last glacial period.[1][2]
The term "driftless" indicates a lack of gla-
cial drift, the material left behind by retreat-
ing continental glaciers.
Geological formation
Typical terrain of The Driftless Area as
viewed from Wildcat Mountain State Park in
Vernon County, Wisconsin
Retreating glaciers leave behind silt, clay,
sand, gravel, and boulders — called drift.
Glacial drift includes till (unsorted material)
and outwash (layers deposited by meltwater
streams)".[3] While some glacial drift has
been discovered, this is said to be of "Pre-
Illinoian age" about 500,000 years old.[2][4][5]
What is clear is that the region has been
subject to the regular catastrophic effects of
glacial
lake outburst floods involving the
cataclysmic collapse of ice dams holding in
such bodies as Glacial Lake Agassiz, Glacial
Lake Grantsburg, and Glacial Lake Duluth
(see Jökulhlaup).
The earlier local phases of the Wisconsin-
an glaciation are poorly understood, but the
last involved several major lobes, the Des
Moine