The Driftless Area: Wisconsin's strange geology

Image: The Baraboo Range, a Creative Commons Attribution Share-Alike (2.0) image from crisp_air's photostream

On Wednesday, I traveled to Madison, Wisconsin, to give a talk based on my book, Before the Lights Go Out. I took the train to get there, traveling south from Minneapolis along the Mississippi River before jumping the border into Wisconsin at the town of La Crosse.

This isn't a region I've spent much time in before, and I was struck by the landscape, which felt exotic and foreign—adjectives that are seldom applied to southeastern Minnesota and southwest Wisconsin. The Mississippi here looks less like a river and more like a series of interconnected lakes dotted with sandbars, narrow peninsulas, and forested islands. Looking across the water, into Wisconsin, a line of strangely shaped tall hills (or maybe small mountains) run along the shore—all severe, sharp angles covered in a fuzzy looking blanket of trees. It almost looks like somebody cut a patch out of Appalachia and dropped it into the middle of the prairie.

This is the Driftless Area, a part of the upper Midwest that combines some wonderfully weird geology with a truly kick-ass name. I did a little research on the region during the rest of my trip and I wanted to share a couple of the cool things that I learned.

First, about that name …

Image taken by Dandog77. Found on Wikipedia and used via CC license.

The name "Driftless Area" has nothing to do with snow. Instead, it's referring to a different kind of "drift"—a mixture of rocks and gravel, boulders and residue that's normally left behind by retreating glaciers. The geology of the upper Midwest owes much of its shape to the movement of glaciers. Minnesota's 10,000+ lakes, for instance, are largely divots scraped out of the Earth by these massive walls of ice. The depressions later filled with water and became lakes. But the most recent glacial marches to the south—"recent", in this case, meaning things that happened 100,000 years ago—seem to have bypassed the Driftless Area entirely. Because of that, the geography here looks very different compared to the glacier-shaped land around it.

Image: Babson Aerials 9-29-09 Tunnelville Road, a Creative Commons Attribution (2.0) image from usfwsmidwest's photostream

The Baraboo Range is a big part of what makes the Driftless Area look so unique. Here's a fun, new vocabulary word: monadnock. The word refers to solitary mountains, or huge masses of rock rising up out of the middle of a plain. You can find examples of monadnocks all over the world. Basically, they're just places where a hunk of hard, not-particularly-easy-to-erode rock was surrounded by a lot of weaker material. After everything else has washed away over hundreds of thousands of years, you're left with a knob of the hard stuff sticking up all alone.

The Baraboos are a whole collection of monadnocks packed into an area about 25 miles long and less than 10 miles wide. They are the tops of an ancient mountain range—hard quartzite from 500 million years ago that was buried beneath layer upon layer of softer rocks like limestone and sandstone. That material buried the Baraboos, and then it slowly disintegrated, leaving the peaks of what were once massive mountains exposed.

Pictured: Wisconsin. Seriously. Photo taken by Emery. Found on Wikipedia and used via CC license.

For more information:

Check out "Mysteries of the Driftless Zone" a documentary by Untamed Science, which is a production company made up of both scientists and filmmakers. The film is currently in production, but you can watch a couple of preview videos on the site—including one about the cave system in the Driftless Area, which I didn't even get into here.