Libby Reuter and Joshua Rowan
Madison County, Illinois
ABOUT THIS WATERSHED
Horseshoe Lake is the second largest natural lake in the State of Illinois. It was formed centuries ago when floodwaters covered the land that geologists call the American Bottom. As the floodwaters receded, the Mississippi River found a new channel, leaving this oxbow-shape lake unconnected to the main river. Recently, University of Wisconsin researchers discovered evidence of these ancient floods by studying cores of sediment taken from Horseshoe Lake. One flood in about 1200 CE/AD crested near 33 feet, enough water to cover the flat bottomland six miles to Cahokia Mounds, destroying the crops. This new information supports the theory that flooding was the reason the Mississippian people left their metropolis at that time.
HORSESHOE LAKE GROTTO
Just a few feet from young trees separating the Horseshoe Lake Cairn form the water, the knarled roots behind the Horseshoe Lake Grotto Cairn hide a drainpipe peeking out from the earth. There is no contemporary building in or near the trees that would explain the pipe; the history of this site is a mystery.