Ohio Geologic Map

Underneath a widespread cover of young glacial sediment laid down in the last million years, Ohio is underlain by sedimentary rocks older than 250 million years: mostly limestone and shale, laid down in gentle, shallow seas. The oldest rocks are of Ordovician age (about 450 million years), in the southwest; overlying them in a sweep over to the southeast border are (in order) Silurian, Devonian, Mississippian, Pennsylvanian and Permian rocks. All are rich in fossils. See a gallery of Ohio geological attractions.

Deep beneath these rocks is the far more ancient core of the North American continent, sloping away to the Illinois Basin to the southwest, the Michigan basin to the northwest, and the Appalachian Basin to the east. The part that isn't sloping, in the western half of the state, is the Ohio Platform, buried some 2 kilometers deep.

The thick green lines mark the southern limit of continental glaciation during the Pleistocene ice ages. On the north side, very little bedrock is exposed at the surface, and our knowledge is based on boreholes, excavations and geophysical evidence.

Ohio produces a great deal of coal and petroleum as well as other mineral products such as gypsum and aggregate.

Find more geologic maps of Ohio at the Ohio Geological Survey website.

More about Ohio Geology

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About Cleveland
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Ohio Maps
Ohio Geography, State Symbols & Facts
Ohio National Parks
Ohio State Parks
Ohio Campgrounds
Ohio Hunting
Ohio Skiing
Ohio Archaeology