Surface Geologic Map of Iowa
Image courtesy Iowa Geological Survey Bureau (fair use policy)
Iowa is almost entirely covered by loose sediments left behind by the continental glaciers of the Pleistocene ice ages. So like many other Midwestern and northern states, Iowa needs two maps, one for the buried bedrock and one for the surface deposits. Only in the Paleozoic Plateau, in the Driftless Area, is bedrock widespreadbut there you can visit the classic strata of the Mississippian sequence along the Mississippi River with their associated fossiliferous beds and cave-bearing karst terrain.
The latest advance of the ice, known as the Wisconsinan event, left behind the hummocky moraine country of the Des Moines Lobe. The rest of the state is covered with deposits from earlier episodes. The southern region is deeply dissected by later erosion, while the northern areas on either side of the Des Moines Lobe were leveled by permafrost conditions during the late ice age. Wind erosion of the dusty glacial drift left widespread, thick beds of loesspure silt, valued for farmlandall around the state, particularly in the Loess Hills along the Missouri River valley. The modern Missouri and Mississippi rivers have built fairly narrow alluvial plains in the years since the glaciers left.
Unlike the stony glacial lands of New England, the ice ages have been kind to Iowa. The Iowa Geological Survey Bureau celebrates the variety of glacial landforms found around this interesting state.
See a somewhat larger version with the original image.
More Iowa resources on About.com:
Iowa Geography & Maps
Iowa State Symbols & Facts
Iowa National Parks
Iowa State Parks
Iowa Scenic Roads
Iowa Family Destinations