THE QUATERNARY GEOLOGY OF WISCONSIN (1:500,000)

This poster presents a new 1:500,000 map of the Quaternary geology of Wisconsin. Pre-existing statewide Quaternary mapping at this scale is limited to maps by Chamberlin in 1881 and Hadley and Pelham in 1976. The new map was made by compiling previous mapping at 1:100,000 scale for 44 of Wisconsin’s 72 counties, along with partial mapping at the 1:100,000 scale and/or mapping at the 1:250,000 scale for 13 additional counties. Some areas had no prior mapping available. New map units were developed for the 1:500,000 scale and are divided into glacial and nonglacial sediment characterized by lithology and subdivided by geomorphology. Glacial sediment is mapped at the formation level following the WGNHS Lexicon of Pleistocene Stratigraphic Units. Color hue is used to differentiate among the various glacial formations by source areas with green groupings derived from the Lake Superior basin, blue groupings from the Lake Michigan basin, and purple groupings for sediment derived from the west. The darkest colors are assigned to moraines and hummocky till that mark the extent of glacial lobes of the late Wisconsin Glaciation. Other Quaternary units are generally shown in warm colors including meltwater-stream sediment, lake sediment, eolian sediment, colluvium, and alluvium that includes some small areas of terraces along major river valleys. The Driftless Area in southwestern Wisconsin shows the dendritic patterns of colluvium along branching alluvial tributaries with windblown silt on the uplands. Some large deposits of organic sediment and areas of exposed or thinly covered bedrock are included at this scale. The map will be available with GIS data formatted according to the USGS standard Geologic Map Schema (GeMS).