The Land - Geograpic basics
Arguably, the most notable event to define Wisconsin’s geography was the “Wisconsin Glaciation.” It radically altered the geography of North America north of the Ohio River. It consisted of a major advance of the North American Laurentide ice sheet, which covered most of Canada and a large portion of the US.
This Glaciation Episode extended from about 110,000 to 10,000 years ago. It is important to note that this was the most recent glacial period, or said differently, the last glacial period. The Great Lakes resulted from this episode. So did Niagara Falls. It carved the gorge that is now the Upper Mississippi River.
One of the more incredible features of this glaciation was that the ice sheet did not cover the entire state. In layman’s terms, there was a large hole of geography never covered by the ice. It is known as the Driftless Area; that is, the glacier, when it withdrew, did not leave any drift there because it did not cover this area. This area extended into parts of Minnesota, Iowa and Illinois as well. Certainly in the case of Wisconsin, it left a steep and rugged landscape untouched, something most noticeable when traveling through the southwest region of the state.
The Driftless Area extends into Minnesota, Illinois and Iowa. It is that part of the American Midwest that was never glaciated. The rugged terrain is due both to the lack of glacial deposits, or drift. The Area contains deeply-carved river valleys and elevations ranging from 603 to 1,719 feet.
I wish to show you two more maps that will help you understand the state’s geography well.
The scientists have divided the state into five Geographic Provinces, as shown here. If you look carefully, you can see a greenish dotted line outlining the edge of the Driftless area. In my travels, I have found understanding this map to be most useful
This second map is as useful as its predecessor, maybe more so. Here, the scientists have defined Ecological Landscapes of Wisconsin’s Lake Superior Basin. This map has a lot to do with the interplay between unique soils, hydrology and forest cover. Most of this is the result of the glaciation episode.
In this eastern sector of the state, there are three major escarpments, the result of glacial sculpture and erosion. They are the Magenisan, Trenton and Niagara escarpments. An escarpment is a long, steep slope, especially at the edge of a plateau or separating acres of land at different heights.
Speaking quite broadly, the Magnesian Escarpment divides the Eastern Ridges and Lowlands from the Central Plain Geographic Provinces. It rises to about 724 ft. up in Marinette County and then to about 1240 ft. in southern Dane County. The photos of Gibraltar Rock I have presented is in Columbia County, on the northern edge of Dane County.