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Geologic Map of Iowa

page 4


Iowa's bedrock is exposed at the surface in the ribbons of ages that cross the state. Each color represents deposits of a different age. 

At Burlington, Le Grand, Sioux City, and across the state, we can see exposed layers rock--limestone, sandstone, dolomite, siltstone and shale. These layers are not the same age or thickness in all parts of Iowa. Because of uneven deposits and erosion they thicken and thin, disappear and blend across the state.

The map colors represent rock ages and their distribution as exposed rock beneath the glacial till. The display of the colors is affected by the angle the rock lies within the earth, structure, and the extent of erosion of the surface exposure. Stream valleys cut through younger rock and expose older as the upper layers are eroded away. Erosion may leave remnants of younger or older rock as "islands" in areas of another age.
The geologic map provides a quick way to determine what rocks are exposed near the surface, although they may be covered by glacial deposits, in any area of Iowa.

The Iowa Geological Survey Bureau, Department of Natural Recourses, provides copies of the Iowa geological map and physiological region map on their website at:


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