The Driftless Area, also known as Bluff Country and the Paleozoic Plateau, is a topographic and cultural region in the Midwestern United States that comprises southwestern Wisconsin, southeastern Minnesota, northeastern Iowa, and the extreme northwestern corner of Illinois. The Driftless Area is a USDA Level III Ecoregion: Ecoregion 52. The Driftless Area takes up a large portion of the Upper Midwest forest–savanna transition. The eastern section of the Driftless Area in Minnesota is called the Blufflands, due to the steep bluffs and cliffs around the river valleys. The western half is known as the Rochester Plateau, which is flatter than the Blufflands. The Coulee Region is the southwestern part of the Driftless Area in Wisconsin. It is named for the lack of glacial drift in the area: the silt, gravel, and rock left behind by glaciers that can be found in other parts of Wisconsin.
The Driftless Area was never covered by ice during the Last Glacial Period, so the area lacks the characteristic glacial deposits known as drift. Its landscape is characterized by steep hills, forested ridges, deeply carved river valleys, and karst geology with spring-fed waterfalls and cold-water trout streams. Ecologically, the Driftless Area's flora and fauna are more closely related to those of the Great Lakes region and New England than those of the broader Midwest and central Plains regions. The steep riverine landscape of both the Driftless Area proper and the surrounding Driftless-like region is the result of early glacial advances that forced preglacial rivers, which flowed into the Great Lakes, southward, causing them to carve a gorge across bedrock cuestas, thereby forming the modern incised upper Mississippi River valley. The region has elevations ranging from 603 to 1,719 feet (184 to 524 m) at Blue Mound State Park, and together with the Driftless-like region, covers .U.S. Department of Agriculture Natural Resources Conservation Service. Driftless Area Landscape Conservation Initiative; . Retrieved August 25, 2017.
Geologic origin
Retreating glaciers leave behind material called drift composed of silt, clay, sand, gravel, and boulders. Glacial drift includes unsorted material called till and layers deposited by meltwater streams called outwash."The Driftless Area" , Minnesota Conservation Volunteer, March 2007 (popular article from the Minnesota Department of Natural Resources (MDNR)), Retrieved July 7, 2007 While drift from early (pre-Illinoian) glaciations has been found in some parts of the region,"Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin: Section IV. Driftless Area" , USGS, Retrieved July 13, 2007; another government site, "Driftless Area Initiative", USDA, retrieved July 15, 2007, gives and "Yellow River State Forest" , Iowa Department of Natural Resources (IDNR), Retrieved July 7, 2007Byron Crowns. "Wisconsin through 5 Billion Years of Change", Wisconsin Earth Science Center, 1976, Wisconsin Rapids, Wisconsin, p. 131, much of the incised Paleozoic Plateau of Wisconsin and northwestern Illinois has no evidence of glaciation. The Ice Age National Scenic Trail is famous for taking hikers along the southernmost point of the last ice age's glacial lobe, which does not include the present city of Milwaukee.
Numerous glacial advances throughout the world occurred during the most recent Quaternary glaciation (also known as the Pleistocene glaciation). The Upper Midwest and Great Lakes region of North America was repeatedly covered by advancing and retreating glaciers throughout this period. The Driftless Area escaped much of the scouring and depositional action by the continental glaciers that occurred during the Last Glacial Period, which produced significant differences in the topography and drainage patterns within the unglaciated area compared to adjacent glaciated regions.
The region has been subjected to large floods from the melting Laurentide ice sheet and subsequent catastrophic discharges from its proglacial lakes, such as Glacial Lake Wisconsin, Glacial Lake Agassiz, Glacial Lake Grantsburg, and Glacial Lake Duluth.
The last phases of the Wisconsin glaciation involved several major lobes of the Laurentide Ice Sheet: the Des Moines lobe, which flowed down toward Des Moines 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 Watersmeet Dome, an ancient uplifted area of Cambrian rock underlain by basalt in northern Wisconsin and western upper Michigan. The southward movement of the continental glacier was also hindered by the great depths of the Lake Superior basin and the adjacent highlands of the Bayfield Peninsula, Gogebic Range, Porcupine Mountains, Keweenaw Peninsula, and the Huron Mountains along the north rim of the Superior Upland bordering Lake Superior. 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.
Another factor that may have contributed to the lack of glaciation of the Driftless Area is the fractured, permeable bedrock within the Paleozoic Plateau underlying it, which would have promoted below-ground drainage of subglacial water that would otherwise have lubricated the underside of the glacial ice sheet. The dewatering of the underside of the ice sheet would have inhibited forward movement of the glacier into the Driftless Area, especially from the west.
In the adjacent glaciated regions, the glacial retreat left behind drift, which buried all earlier topographical features. Surface water was forced to carve out new stream beds."Native American use of the Mississippi River" . Archaeology Education Program, vol. 22, no. 2 (Fall 2004):1. Retrieved January 25, 2018. This process was absent in the Driftless Area, where the original drainage systems persisted during and after the Last Glacial Period. Water erosion continued carving the existing gullies, ravines, stream beds, and river valleys ever deeper into the paleozoic plateau, following the original drainage patterns.
Characteristic landforms
Geology
Overall, the region is characterized by an eroded plateau, with bedrock overlain by varying thicknesses of loess. Most characteristically, the branching river valleys are deeply dissected. The bluffs lining this reach of the Mississippi River climb to nearly . In Minnesota, pre-Illinoian-age till was probably removed by natural means before the deposition of loess. The valley walls' sedimentary rocks date to the Paleozoic Era and are often covered with colluvium or loess.Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin, Section IV, Driftless Area , National Park Service, Retrieved July 9, 2007 (A statement from this copyright-free site has been freely paraphrased.) 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 in south central Wisconsin, consists primarily of Precambrian quartzite and rhyolite. The area has not undergone much tectonic action, as all the visible layers of sedimentary rock are approximately horizontal.
Karst topography is found throughout the Driftless area. This is characterized by caves and cave systems, disappearing streams, blind valleys, underground streams, sinkholes, springs, and cold streams. Disappearing streams occur where surface waters sink down into the earth through fractured bedrock or a sinkhole, 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 result from the collapse of a cave's roof, and surface water can flow directly into them. Disappearing streams can re-emerge as large, cold springs. Cold streams with cold springs as their sources are superb trout habitat. Due to the rapid movement of underground water through regions with karst topography, groundwater contamination is a major concern in the Driftless area.
Rivers
The Mississippi River passes through the Driftless Area between and including Pool 2 and Pool 13.
As rivers and streams approach their confluence with the Mississippi, their canyons grow progressively steeper and deeper, particularly in the last in their journey to their mouths. The change in elevation above sea level from ridgetops lining a stream to its confluence with the main-stem Mississippi can reach well past in only a few miles. The Waukon Municipal Airport is reliably established as being above sea level. The Army Corps of Engineers maintains a river level in Pool 9 of about above sea level, which covers Lansing. Maps and signs issued by the Iowa Department of Transportation indicate Waukon and Lansing are apart on Iowa Highway 9. This is a drop of more than in less than (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). In August 2018, the region yet again experienced record-breaking flooding in valley towns such as Coon Valley, Wisconsin, La Farge, Wisconsin, and Viola, Wisconsin. The Kickapoo River flood stage is 13 feet but was recorded as high as 23 feet during the 2018 flood which was declared a statewide emergency. Many community members were rescued by boats sent by the Wisconsin Department of Natural Resources. Days later, when two dams in Ontario, Wisconsin broke, it produced flood water downstream in Readstown, Wisconsin, Soldiers Grove, Wisconsin, and Gays Mills, Wisconsin.