Bedrock topography of southwest Iowa

The bedrock in Iowa (Hershey, 1969) is generally overlain by unconsolidataed deposits consisting of glacial drift, alluvium, and loess. Loess deposits are most extensive in areas bordering the Missouri River flood plain, attaining a thickness of over 200ft in some places. The total thickness of the unconsolidated sediments ranges from less than 1 ft to more than 450 ft. The configuration of the underlying bedrock surface is the result of a complex system of ancient drainage courses that were developed during shorter, but more intense, periods of interglacial erosion.