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 Ohio resources on About.com:
Ohio Geography, State Symbols & Facts
Ohio National Parks
Ohio State Parks