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 part 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.
At the risk of oversimplifying, I will simply say that there were multiple ice sheets involved in multiple glacial events. The Laurentide ice sheet covered most of Canada and the northern US. A Greenland Ice Sheet covered it, etc. The point I wish to highlight by this map is that just west of Chicago, you can see a blank spot. For reasons I will have to leave you to study, that is an area the glacier did not cover, to wit, the Driftless areas. Why not? A mystery to me.
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.
This map does not show the full length of the escarpment, but you can see it is west of Ripon, which is west of Lake Winnebago, and quite pronounced between Berlin to the north and Green Lake to the south.
The Niagara Escarpment, marked in red, is a landform called a cuesta and it travels from Niagara Falls, New York in a semi circle westward through eastern Wisconsin. It runs predominantly east/west from New York State, through Ontario, Michigan, Wisconsin and Illinois. The escarpment is most famous as the cliff over which the Niagara River plunges at Niagara Falls, for which it is named.
In Wisconsin, it lies largely east of Lake Winnebago and up through Door Peninsula and County. Door Peninsula separates Green Bay and Lake Michigan. Limestone outcroppings of the Niagara Escarpment are visible on both shores of the peninsula, but are larger and more prominent on the Green Bay. When talking about Green Bay I am talking about the bay of water, not the city.
The Niagara Escarpment consists of a gently-sloping layer of rock forming a ridge. One side of the ridge has a gentle slope, a so-called dip slope that is essentially the surface of the rock layer. The other side is a steep bluff.
You may wish to refer back to these maps as you view photography of the landscapes throughout the state that I show.
I think I would say that since the arrival of people of European descent to the region, arguably one of the most notable changes to the states geography has been the manner in which the state’s many rivers have been dammed, oft creating lakes, oft creating electrical energy, oft running manufacturing plants.
You’ll see in my photography I get a real kick out of these dams, which range in size from massive to very small.