Geologic Map of Missouri
Image courtesy Missouri Department of Natural Resources (fair use policy)
Missouri contains the largest of the gentle arches in the American midcontinent—the Ozark Plateau. It has the the largest outcrop area of Ordovician-age rocks in the country (beige). Younger rocks of Mississippian and Pennsylvanian age (blue and light green) occur to the north and west. On a small dome at the east end of the plateau, rocks of Precambrian age are exposed in the St. Francois Mountains.
The southeast corner of the state lies in the Mississippi Embayment, an ancient zone of weakness in the North American plate where once a rift valley threatened to turn into a young ocean. Here, in the winter of 1811–12, a terrible series of earthquakes rolled through the thinly inhabited country around New Madrid County. The New Madrid quakes are thought to be the most severe seismic event in American history, and research into their cause and effects continues today.
Northern Missouri is carpeted with Ice Age deposits of Pleistocene age. These consist mostly of till, the mixed debris lifted and dropped by glaciers, and loess, thick deposits of windblown dust that are known around the world as excellent farming soils.
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More Missouri resources on About.com:
About St. Louis
About Kansas City, Missouri
Missouri Maps
Missouri Geography, State Symbols & Facts
Missouri National Parks
Missouri National Forests
Missouri Campgrounds
Missouri Scenic Roads
Missouri Bed & Breakfasts
Missouri Archaeology
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