At the Wisconsin Science Fest yesterday I learned that the Wisconsin River used to flow the other way. Wow!
The upper Mississippi River from Minnesota used to hang a left at the Wisconsin/Iowa border and headed to the St. Lawrence seaway instead of connecting to the lower Mississippi. But the Ice Age glaciers that covered eastern Wisconsin effectively dammed that eastward flow, so the river was forced to instead carve through the hills near Wyalusing State Park and the Dubuque area to connect to watersheds to the south.
The evidence is: 1) core samples show the bedrock under the Wisconsin River generally slopes east, as opposed to the present-day surface which slopes west, 2) tributaries into the Wisconsin generally point east, 3) the Wisconsin river valley is very wide for today’s comparatively small river, 4) in contrast the Mississippi channel just south of the mouth of the Wisconsin is recently carved with narrow steep banks.
I didn’t catch the name of the scientist at the expo but after looking at the https://wgnhs.uwex.edu/ staff page, maybe it was Liz Ceperley? It looks like this research is led by UW Prof Eric Carson