Bedrock Topography Beneath the Des Moines Lobe Drift Sheet, North-Central Iowa

The bedrock surface beneath the Des Moines Lobe Drift Sheet in Iowa contains the junction of the paleo-drainage divides between pre-glacial north, southeast and southwest flowing drainage. The bedrock uplands containing these divides have controlled the shape and location of the Des Moines Lobe as well as the location and shape of the end moraines upon the drift sheet. The total drift thickness beneath the lobe is commonly 100 to 150 feet but ranges from 20 to 500 feet. The relatively uniform thickness of the drift means that the surface topography mimics the bedrock topography. Hummocky end moraines and three of Ruhe\u27s end moraines appear to overlie bedrock slopes opposed to glacial flow and bedrock uplands, whereas minor moraine topography and the Bemis end moraine overlie bedrock slopes on lee sides of uplands