Formation

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 includes areas of southeast Minnesota, northeast Iowa and northwest Illinois (see map at right). This region includes elevations ranging 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.

The term "driftless" indicates a lack of glacial drift, the material left behind by retreating 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)".

While some glacial drift has been discovered, this is said to be of "Pre-Illinoian age" about 500,000 years old.

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 Wisconsinan glaciation are poorly understood, but the last involved several major lobes, the Des Moines lobe, which flowed down to Iowa's capital city on the west, the Superior lobe (and its sublobes) on the north and the Green Bay lobe and Lake Michigan lobes on the east. The northern and eastern lobes were in part diverted around the area by the Wisconsin Dome, an exceedingly ancient uplifted area of Cambrian rock underlain by basalt. The Green Bay and Lake Michigan lobes were also partially blocked by the bedrock of the Door Peninsula, which presently separates Green Bay from Lake Michigan. In earlier phases of the Wisconsinan, the Driftless Area was totally surrounded by ice, with eastern and western lobes joining together to the south of it.

In the adjacent glaciated regions, the glacial retreat left behind drift which buried all former topographical features. Surface water was forced to carve out new stream beds.

Characteristic Land Formations of the Driftless Area

Geology

Overall, the region is characterized by an eroded-down plateau with bedrock overlain by varying thicknesses of loess. Most characteristically, the river valleys are deeply-dissected. The bluffs lining this reach of the Mississippi River currently climb to not quite 600 feet (180 m). In Minnesota, Pre-Illinoian age till was probably removed by natural means prior to the deposition of loess. The sedimentary rocks of the valley walls date to the paleozoic and are often covered with colluvium or loess. Bedrock, where not directly exposed, is very near the surface and is composed of "primarily Ordovician dolomite, limestone, and sandstone in Minnesota, with Cambrian sandstone, shale, and dolomite exposed along the valley walls of the Mississippi River." In the east, the Baraboo Range, an ancient, profoundly eroded monadnock has some of the most ancient exposed rock in North America, primarily quartzite and rhyolite. The area has not undergone much seismic action, as all the visible layers of sedimentary rock are approximately horizontal.

Karst topography is found throughout the Driftless. This is characterized by caves and cave systems, disappearing streams, blind valleys, underground streams, sinkholes, springs, cold springs and cold streams. Disappearing streams are when surface waters sinks down into the earth through fractured bedrock, either joining an aquifer, or becoming an underground stream. Blind valleys are formed by disappearing streams and lack an outlet to any other stream. Sinkholes are the result of the collapse of the roof of a cave, and surface water can flow directly into them. Disappearing streams can re-emerge as often powerful springs, often having been cooled down by the water's journey through the earth. Cold streams with cold springs as it sources are noted as superb trout habitat. All of these features are found in the Driftless area.

Rivers

The Mississippi River passes through the Driftless Area between and including Pool 2 to Pool 13.

As rivers and streams approach their confluence with the Mississippi, their canyons grow progressively steeper and deeper, particularly in the last 25 or so miles (40 km) in their journey to their mouths. The change in elevation above sea level from ridgetops lining a stream to its confluence with the Big River can reach well past 650 feet (200 m) in only a few miles. The Waukon Municipal Airport is reliably established as being 1281 feet (390.4 m) above sea level. The Army Corps of Engineers maintains a river level in Pool 9 of about 619 feet (189 m) above sea level, which covers Lansing. Maps and signs issued by the Iowa Department of Transportation indicate Waukon and Lansing are 17 miles (27 km) apart on Iowa Highway 9. This is a drop of more than 660 feet (200 m) in less than 20 miles (and this along a very minor tributary of the Mississippi). "The role of isostatic rebound on the process of stream incision in the area is not clearly understood."

There are many small towns in the Driftless Area, especially in river valleys, at or upstream from the Mississippi. Small towns in a deep steep valley going down to the Mississippi are at risk every 50 to 100 years or so of a major flood, as with the wreck of Gays Mills, Wisconsin in August 2007, or the holding of the levee in Houston, Minnesota (on the South Fork Root River) at the same time. Metropolitan areas have flood walls (See 2007 Midwest flooding).

The history of this portion of the Upper Mississippi actually dates back to an origin "as an ice-marginal stream during what had been referred to as the “Nebraskan glaciation.”" Current terminology would place this outdated and abandoned period in the Pre-Illinoian Stage. The level of erosion often exposes Cambrian limestone of about 510 million years of age.

The Mississippi River trench is one of the few places in the Driftless Area where the bedrock is very deep below the surface, and is overlain by large amounts of sediment. As home to the formation of a substantial portion of the gorge of the Upper Mississippi, this enormous quantity of sediment goes down at least 300 feet (91 m) under the present riverbottom at the confluence of the Wisconsin River. In contrast, as the River exits the Driftless Area "between Fulton and Muscatine, [... (Pool 13)], it flows over or near bedrock.". "The course of the upper Mississippi River along the margin of the Driftless Area of southeastern Minnesota is believed to have been established during pre-Wisconsin time when a glacial advance from the west displaced the river eastward from central Iowa to its present position."

Other rivers affected by this process are:

In Wisconsin, the Chippewa, Trempealeau, La Crosse, Black, and the Wisconsin River, along with its tributary, the Kickapoo River;
In Minnesota, the Whitewater, Cannon, Zumbro, and Root rivers;
In Iowa, the Upper Iowa, (Paint Creek may also be mentioned), Yellow, Turkey, and Maquoketa rivers;
In Illinois, the Apple River and the Galena River (a.k.a. the Fever River).

The Saint Croix in Wisconsin is another important river in the Driftless Area, as it was the outlet for Glacial Lake Duluth, forerunner to Lake Superior, when the eastern outlet was blocked by the continental ice sheet. These rivers all have deep, dramatic canyons giving testimony to the immense quantity of water which once surged through them. The Wisconsin River drained Glacial Lake Wisconsin. Glacial River Warren, whose bed is now occupied by the Minnesota River, drained the colossal Glacial Lake Agassiz. There was ample water to dig a very deep, hundreds-of-miles-long gash into the North American bedrock.

Ecosystem

Prior to European settlement in the 19th century, the vegetation consisted of tallgrass prairie and bur oak savanna on ridgetops and dry upper slopes, sugar maple-basswood-oak forest on moister slopes, sugar maple-basswood forests in protected valleys and on north-facing slopes, wet prairies along the rivers, and some mesic prairie on the floodplain further back from the river. There were probably also oak forests that contained no sugar maple. Marsh and floodplain forests were also common on river flood plains. Prairie was restricted primarily to the broader ridge tops, which were unfavorable sites for trees due to thin soils and shallow bedrock, rapid drainage, and desiccating winds; all these conditions were also good for carrying fires across the landscape. Prairies also occurred on steep slopes with south or southwest aspect (see Goat prairie). Natural fire, which has long been vigorously suppressed, was essential for the regeneration of such prairies.

The Midwest Driftless Area Restoration Effort is a multi-agency cooperative effort to restore the landscape. The main issues are water pollution, from agricultural and animal runoff, and erosion. Water pollution is particularly critical in karsted regions such as this, in that it can degrade or destroy prime cold water fish habitat. Soil erosion, a bad thing in general, presents the Army Corps of Engineers with a particular problem, in that it requires them to dredge the Mississippi to keep the Mississippi River shipping channels open. Trout Unlimited is part of this effort, if only because of the superb cold-water streams the region supports. A symposium was held in October 2007 in Decorah, Iowa "to share the results of research, management and monitoring work in the Driftless Area." The Nature Conservancy is also interested.

Iowa Pleistocene snail. An apparently unique feature of the Driftless Area are small, isolated ecosystems termed algific talus slopes. These refugia create cool summer and fall microclimates, which host species usually found further north. It contains at least one endangered species, the Iowa Pleistocene Snail, and a threatened plant, the Northern monkshood. The Driftless Area National Wildlife Refuge was primarily carved out of the Upper Mississippi River National Wildlife and Fish Refuge in order to protect these species and their associated ecosystems.

The list of protected areas in the region is extensive. Most of them, however, were established for reasons having little to do with being in the Driftless, but nonetheless incidentally locked up some valuable parcels.

A particularly noteworthy annual event is the rising of fishflies, a kind of mayfly endemic to the Mississippi valley in the region. These are aquatic insects who, attracted to light, rise by the millions as adults to mate, only to die within hours.

Wildlife is abundant. Opportunities for hunting whitetail deer and wild turkey are extensive. Fishing, particularly for brown trout in tributaries, as well as species such as channel catfish in the Mississippi is available, while ice fishing in winter is something of a regional sport.

Other Characteristics

The Driftless Area is part of the Mississippi Flyway. Many birds fly over the river in large flocks, going north in spring and south in autumn.

There are very few natural lakes in the region, these being found in adjoining areas of glacial till, drift and in moraines; the region is extraordinarily well drained, and there is rarely a place where even a pond can naturally form. There are also very few dams in that the valley walls and floors are very often fissured or crumbly, or very porous, providing very poor anchors for a dam or making it difficult to keep any kind of reservoir appropriately filled. There are no real waterfalls, but some very strong springs bear the name.

A modern, man-made characteristic is the comparatively twisty nature of highways in the region, like in Kentucky, in contrast to the usually rigid east-west/north-south alignment elsewhere in the Midwest. Here, the roads switchback up stream valleys or travel over ridgetops. The route of U.S. Highway 20 through the Driftless, and particularly in Illinois, is a good example.