A few months ago (it is now August 3rd, 2008) I was looking at land in Wisconsin between Chicago and Minneapolis in Google Earth. I noticed what appeared to be a circular area with its north point at Eau Claire, its east point at roughly Jackson or Black River Falls, its west point near Winona Minnesota and its south point on Wisconsin Highway 54.
Having driven to Minneapolis from Chicago hundreds of times I have always been interested in the area starting at Black River falls going west on Interstate 94. It is some of the prettiest country on the drive. As you approach Black River Falls, there is a ridge of hills. There is also a ridge of hills at Eau Claire. While investigating more closely in Google Earth and Google Maps, I noticed that there is essentially a ring road going all the way around the “crater”. Theorizing that these ridges of hills were the vestigial crater rim, I drove around about 270 degrees of the “rim”. It is hard to tell from the ground, but it is certainly plausible that there is a rim around this geological feature, and this would help explain why there is essentially a ring of roads around the rim.
If this is a crater, it is very large with a diameter around 60-70 miles. Below are two images from Google Earth and Google Maps. In addition there are four NASA World Wind images kindly sent to me by Dr. Kord Ernstson of impact-structures.com.
Now all I have to do is figure out how to gather the evidence that will prove the structure is indeed an impact structure. Should be fun. Camping and hiking anyone?