Detailed evaluation of pedogenic, geologic, and paleomagnetic properties has enabled the identification of several pre-Wisconsinan stratigraphic units in west-central Wisconsin. The older unit is the Pierce Formation, consisting of the Hersey Member, which contains gray, calcareous, loam-textured till, and the Kinnickinnic Member, which contains rhythmically bedded lacustrine sediments deposited in a complex network of proglacial lakes. Paleomagnetic and pedogenic data from the Pierce Formation suggest that the Hersey Member was deposited during either the Emperor reversed event or the Matuyama reversed polarity epoch and that deposition of the Kinnickinnic Member spanned either the Emperor-Brunhes or the Matuyama-Brunhes boundary ∼460,000 or 730,000 B.P., during Pre-Illinoian time. The younger, pre-Wisconsinan unit is the River Falls Formation, which contains a reddish-brown, sandy-clay-loam-textured till and associated sand and gravel. Soil-profile development and regional correlation indicate that this unit is Illinoian in age. These results contradict previously published studies which suggested that tills of the Hersey Member and the River Falls Formation were deposited by the same Wisconsinan ice advance and that no pre-Wisconsinan sediment is present in western Wisconsin.

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