The southern boundary is the southern edge of the lake plain where is abuts Des Moines Lobe ground moraines and end moraines. The eastern boundary separates that portion of the lake plain that is primarily peatland from wet to dry mineral sediments. This subsection is characterized by a flat, poorly drained lake plain. Local topographic relief is less than 50 feet on most of the plain. Upland sites are commonly vegetated by aspen-birch and jack pine.
Sediments vary in texture across the extensive lake bed.
Drift is up to 300 feet thick at the western edge of the basin. There are a greater percentage of organic soils in the center of the lake basin, with increased amounts of poorly drained mineral soils near the edges. Hemists occupy the center of the lake basin, whereas Aqualfs and Aquents are along the margins of the basin. The growing season is short, from 98 to 111 days, with the shortest growing season near the eastern edge of the subsection. This subsection is virtually level and the drainage network reflects that.