The Iowa Geological Survey at the University of Iowa, a division of the Iowa Department of Natural Resources, provides the following resources. They have been integral in assisting our research efforts. The following selections have individual web page addresses at the end of each section. Click here for a link to the Iowa Geological Survey.
PHYSIOGRAPHY OF IOWA
The following is a brief summary of the bedrock history and development of the present surface. At the close of the Cretaceous Period the area which is now Iowa was a land surface. The soft Cretaceous deposits and older rocks were subjected to erosion. During the long Tertiary Period all the land was eroded to a surface with gentle slopes and a relief of about 200 feet. Before the end of the Tertiary time, change in the relative elevations of land and sea caused the streams to be rejuvenated and they developed new valleys. At the new grade, the streams widened their valley floor and weathering reduced the wall slopes to form a more rugged topography than before but still one with moderate slopes and with flat-topped divides at the level of the older surface. The new level is about 200 feet lower; this relief, added to that on the older surface, gives a total relief of about 400 feet. Over such a surface came the first ice sheet of the Pleistocene. The melting of the ice and dropping of the glacial debris left a new surface – a drift surface – superimposed over the bedrock surface. New drainage was inaugurated. This was modified by succeeding ice sheet invasions that buried the new valleys and more deeply covered the preglacial surface.
Today, Iowa is a prairie state having a generally moderate relief and gentle slopes. In some places there are broad uplands, in other places the valley floodplain is conspicuous. In general, the state is well drained by tributaries of the Mississippi and Missouri Rivers at its borders. Some parts of the state show extensive erosion, whereas other parts show little erosion and have distinctive constructional features. It is difficult to say which is the more important in development of the topography – erosion or deposition. However, the origin of the present surface is related very closely to the glacial history of Iowa. Several kinds of topography can be differentiated. The Mankato and Cary drift in northcentral Iowa are depositional terrain. So are the alluvial bottoms of the Mississippi and Missouri Rivers and the loess deposit bordering the Missouri River flatland. The Mankato and Cary surfaces have some of the characteristics of extreme youth of the erosion cycle of glaciated area with valleys just being formed and relatively poor drainage. The surface of the Kansan drift area is much more rolling and approaches the stage of maturity. The Iowan and Tazewell surfaces are intermediate in development but probably more erosional than depositional. In the “driftless area” of northeast Iowa the surface is even more mature.
Iowa’s Stratigraphic Column Text
Click here to view a text version of Iowa’s stratigraphic column. By clicking on any system name you will be taken to a list of Iowa Geologic Survey publications on that system.
Stratigraphic Column of Iowa, 2004
Click here to view the geological bedrock column of Iowa.
Bedrock Geology map of Iowa, 1998
Click here to view a state-wide bedrock map of Iowa.
Landform Regions of Iowa
Iowa is composed of a variety of landscapes or landforms. These are the surficial expressions of geologic processes included in the study know as geomorphology. Please see the web page on the OSA web site entitled Geoarchaeology in Iowa.
Landform Regions of Iowa, 2000
Click here to view the Landform Regions of Iowa produced by the Iowa Geological Survey Bureau.
Regional Bedrock Maps and Descriptions
The 1998 bedrock map is also tied to individual regional bedrock maps currently under production by the Iowa Geological Survey. These maps afford a more detailed view of smaller regions and are accompanied by a through review of previous research and current understandings. Insets identify shallowly buried and surface bedrock outcrops.
Bedrock geology of northwest Iowa, Digital geologic map of Iowa, Phase 1: Northwest Iowa, B. J. Witzke, G. A. Ludvigson, R. R. Anderson, B. J. Bunker, M. K. Slaughter, J. D. Giglierano, J. P. Pope, T. M. Whitsett, and M. J. Bounk, 1997, scale 1:250,000; contract completion report to U.S. Geological Survey for Assistance Award No. 1434-HQ-96-AG-01486, August 1997.
Bedrock geology of northeast Iowa, Digital geologic map of Iowa, Phase 2: Northeast Iowa, B.J. Witzke, G. A. Ludvigson, R. M. McKay, R. R. Anderson, B. J. Bunker, J. D. Giglierano, J. P. Pope, A. E. Goettemoeller, and M. K. Slaughter, 1998, scale 1:250,000; contract completion report to U.S. Geological Survey for Assistance Award No. 1434-HQ-97-AG-01719, August 1998.
Bedrock geology of north-central Iowa, Digital geologic map of Iowa, Phase 3: North-Central Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, G. A. Ludvigson, and S. Greeney, 2001, scale 1:250,000, supported by Cooperative Agreement 00-HQAG-0075, May 2001.
Bedrock geology of south-central Iowa, Digital geologic map of Iowa, Phase 4: South-Central Iowa, J. P. Pope, B. J. Witzke, R. R. Anderson, G. A. Ludvigson, B. J. Bunker, and S. Greeney, 2001, scale 1:250,000, supported by Cooperative Agreement 010-HQAG-0091, July 2002.
Bedrock geology of southwest Iowa, Digital geologic map of Iowa, Phase 5: Southwest Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, and G. A. Ludvigson, 2003, scale 1:250,000, supported by Cooperative Agreement 02-HQAG-0034, September 2003.
Bedrock geology of east-central Iowa, Digital geologic map of Iowa, Phase 6: East-Central Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, and G. A. Ludvigson, 2003, scale 1:250,000, supported by Cooperative Agreement 02-HQAG-0034, September 2003.
Bedrock geology of southeast Iowa, Digital geologic map of Iowa, Phase 7: Southeast Iowa, B. J. Witzke, R. Anderson, and B. J. Bunker, 2004, scale 1:250,000, supported by Cooperative Agreement 03-HQAG-0087, September 2004.