A NEW, PRELIMINARY, LOESS MAP FOR WISCONSIN

As part of a statewide remapping effort being undertaken by the Wisconsin Geological and Natural History Survey at 1:500,000, we are remapping the wind-blown sand and silt deposits of the state. The first and only other such map was produced by Dr. Francis Hole in 1951. Our project updates that map and adds considerable new detail. This poster focuses on the loess component of the map.

Most of our loess data have been derived from loess research by RJS, in which loess samples were collected, and loess thicknesses determined, for > 2700 sites across Wisconsin. During this phase of the project, only loess on stable uplands was examined. Thus, the thickness data we present should be viewed as optimal, or maximal, values; loess thicknesses on side slopes will be thinner. Added to this data set were thickness data from ca. 850 sites visited as part of WGNHS mapping and research, where loess was cored using a geoprobe.

Using NRCS soils data, we first produced a map of the areal coverage of loess. This map makes the important distinctions between landscapes that are nearly completely loess-covered, such as western Marathon County and the southwestern part of the Driftless Area, where >80% of the landscape is loess-covered, and those where loess on stable uplands may be thick, but where most of the landscape is too steep to have retained significant amounts of loess, e.g., Buffalo, Trempeleau, and La Crosse Counties. Other parts of the state contain scattered loess deposits, but only in preferred locations. This map provides a perspective on loess “coverage” that many other such maps ignore.

We have high confidence in the veracity of our loess thickness data, because of the dense network of field-checked sites. Loess is thickest near the Mississippi River valley, but with notable thick (> 100 cm) loess outliers, such as atop the Oneota Cuesta in SE Wisconsin, and in the plains of southeastern Rusk County. New deposits of thin loess are also reported here for the first time, such as those on the Gogebic Iron Range in Iron and Ashland Counties.

We welcome feedback on this new map.