Mapping the presence of red clay subsoil in the Driftless area of Wisconsin, USA

In the unglaciated parts of Southwestern Wisconsin, buried Terra Rossas are commonly found. These clayey, red soils are buried by loess and mainly found on ridges underlain by limestone. They have been eroded during periglacial climates. The red clay has implications for groundwater recharge as well as lateral flow through the landscape. This project focusses on a 50 km2 watershed where some 400 augerhole observations have been made. The landscape was divided into different clusters based on terrain attributes to assess the relationship of environmental covariates with the occurrence of the subsoil clay. Several combinations of landscape attributes were combined but the absence or presence of the Terra Rossa clay is strongly related to elevation. The Terra Rossa is mainly found in the higher parts and absent in the lower parts of the landscape. of unglaciated Southwestern Wisconsin, with ridges dissected by small streams and slopes of varying steepness. The ridges are underlain by limestone, with sandstone often occurring on the slopes. The valleys contain colluvial and alluvial material. Land use is primarily agricultural field crops on the ridges and valleys, with forest on the slopes. Terra Rossa are soils occurring on hard, fractured carbonate rock; they are generally rich in clay and have a reddish color. They are formed through clay formation and carbonate dissolution reactions along with aeolian or other inputs to generate sufficient material for clay formation (Merino and Banerjee, 2008). The Terra Rossa has been forming since before the last ice age, at least over fifteen thousand years ago. During that time it has been subject to mass-wasting during the last ice age, when solifluction and sheet wash were common processes (Frolking et al., 1983; Knox et al., 1990). The landscape was also covered by loess from outwash plains while the aforementioned erosional mechanisms were occurring. This complex history of erosion and deposition makes the presence of Terra Rossa complex to model and predict.