Possible Early Pleistocene Drainage in Wisconsin
The early Pleistocene or pre-Pleistocene drainage system of Wisconsin may have looked like this. Bedrock in the western two-thirds of the state is shown with present outcrop patterns, but the Paleozoic of eastern Wisconsin is shown as it may have been before extensive glacial erosion.
Most of the western drainages are shown as they are at present, along with the present Mississippi, which is probably an early Pleistocene ice-marginal drainage. Whether the Mississippi was the major trunk drainage at this time is not known.
Following a hypothesis advanced by Lawrence Martin, the lower Wisconsin River is shown draining eastward. Unlike most valleys, the Wisconsin River narrows as it goes downstream, becoming narrowest at Boscobel. This suggests that the Wisconsin River may have originally flowed east, but was diverted sometime during the Pleistocene. Martin also suggested the Menominee River once flowed trough the Sturgeon Bay channel as shown.
Created 4 October 2000, Last Update 04 April 2013
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