Yeah, this was news to me too - well sort of. My apologies in advance to our Minnesotan and Iowegian friends that thought they were cool and Driftless like us here in Wisconsin. Well, and Illinois too, but Illinois hardly counts.
Because these areas in Minnesota and Iowa were glaciated, it would not be geologically accurate to identify them as part of the Driftless Area. However, it would be accurate to say those areas have “driftless-style topography”.
Read more at: https://wgnhs.wisc.edu/pubshare/ES057.pdf
Driftless refers to a lack of glacial drift - material carried by glaciers - and areas outside of the true Drifless Area have glacial drift - therefore they are not driftless. What many refer to as the Driftless Area including Minnesota and Iowa is more accurately the Paleozoic Plateau which would also include the TRUE Driftless Area. Rocks of the Paleozoic Era date from 538.8 million years ago (MYA) to about 251.9 MYA. This plateau is largely the sedimentary rocks - dolostone and sandstones - that cover most of the Paleozoic Plateau. Sure, our Mud Duck neighbors have not been glaciated in over 500,000 or more years but they are not driftless. And Iowa? Same thing.
Yes, the landscapes of Iowa and Minnesota's Paleozoic plateau look a lot like the Driftless Area and are landscapes that have largely been carved by rivers, not glaciers. But, again, they are not Driftless - sorry Mud Ducks and the other FIBs for ruining your sense of belonging but science has spoken and you are not Driftless.
This map really shows how the part labeled Driftless Area is the only part of the Paleozoic Plateau that was not glaciated. Previous glaciers - the Pre-Illinoian Glaciations dates back to at least half a million years ago, the more recent Illinoian Glaciation ranged from 300,000 to 130,000 years ago, and the most recent Wisconsin Glaciation had thawed by 10,000 years ago. With the Wisconsin Glaciation being the most recent, it is the most obvious on the landscape. Most of the drift in Wisconsin, Minnesota, and Michigan and large parts of Illinois, Indiana, and Ohio are from this event. And the glacial features - drumlins, kames, eskers, moraines, and most lakes, including the Great Lakes - are the result of the Wisconsin Glaciation.
The Illinoian Glaciation covered much of these same states and even further south. However, there is scant evidence of this glaciation in Wisconsin as the Wisconsin Glaciation rearranged nearly all of the Illinoisan and pre-Illinosian glaciations. And in Minnesota and Iowa, glacial drift from the pre-Illinosian Glaciation is relatively rare and difficult to find.
Note that in his video, the ancient ancestral Mississippi River is probably not correct based on new evidence (read more in a post, When the Wisconsin River Flowed Backwards). However the video does a good - and quick - job of showing the extent of glaciation and the timing of it. The video below is a little longer look at the Driftless Area - Jim Knox gives a good overview of glaciation near the end of the video.
And for an even more in-depth view, watch the lecture that Eric Carson, one of the authors of the paper I highlight in this post, gives about the geology of the Kickapoo River Valley (below).
At the end of the day, for those - like me - that are not geologists - Driftless or Paleozoic Plateau hardly matters. Areas outside of what was truly Driftless have landscapes that are largely the same as those in the Driftless Area. As Eric Carson points out above, even within the true Driftless Area, the landscapes vary. Certainly for the Driftless fly angler, these designations - Paleozoic Plateau vs. Driftless Area - hardly matter but if nothing else it is a bit of fun to take a shot at our non-Driftless neighbors to the West.
Just another quick-hitter for the summer. Go read the original paper and drop your comments below.