Bedrock underlying the subsection is diverse. Ice-stagnation moraines, end moraines, ground moraines, and outwash. Kettle lakes are extremely common within the subsection, on both moraine and outwash deposits. There are more than 400 lakes larger than 160 acres and many more small lakes and potholes, covering 8 to 9 percent of the landscape. Soil textures range from loamy sands and sandy loams on the outwash plains to loams and clay loams on the moraines.
Loamy soils are prevalent.
The irregular topography and the many lakes and wetlands provided a partial barrier to fire, resulting in woodland or forest rather than prairie vegetation. Mixed forests of oaks, sugar maple, basswood, and other hardwoods grew in more fire-protected sites farther east. Tallgrass prairie was present on the more level terrain within the subsection. Fire from the tallgrass prairie to the west was important in the oak savanna and to a far lesser extent in the sugar maple-basswood forest, where windthrow was probably more prevalent and provided greater control on the forest composition. Although large areas are under cultivation, much of the land supports second-growth forest, especially the steeper portions of the landscape.