In eastern Minnesota, loess lies directly upon bedrock. Paleozoic sedimentary rocks crop out in the valley walls, but are generally mantled with colluvium or loess. In most of the section, there is no sign of past glaciation. In these areas, beneath the surface deposit of loess is a layer of limestone residuum, underlain by bedrock. Few natural lakes except for some in the northern part of Sub-subsection IV.2, all on old glacial drift.
Sinkholes are common in the southwest.
Several major rivers flow through the section, forming steep ravines and, on some of the streams, broad alluvial plains. These rivers include the Mississippi, Wisconsin, Kickapoo, Chippewa, Black, Root, Whitewater, Zumbro, and Canon. Cambrian siltstones, sandstones, and shales influence the soil properties. There were probably also oak forests that contained no sugar maple. Marsh and flood-plain forests were also common on river flood plains.