The eastern and southern part of Ohio is dominated by bedrock hills, mostly of Mississippian, Pennsylvanian, and Permian age. Streams have incised deeply into these rocks, which dip gently to the southeast, forming narrow valleys and a landscape with up to 300 feet of relief. Many hills are capped with erosion-resistant beds of sandstone. The western edge of the Appalachian Plateaus is marked by an escarpment formed by the Berea Sandstone.
The western and northern part of the Appalachian Plateaus was glaciated during the Pleistocene Ice Age, which resulted in the hills being of lower relief and the valleys more broad. This region is a subdivision termed Glaciated Allegheny Plateaus. The unglaciated portion of the Appalachian Plateaus is a subdivision termed Allegheny Plateaus and is made up of bedrock of Pennsylvanian and Permian age. The general boundary between the glaciated and unglaciated plateaus is marked by the Allegheny escarpment, which in many areas marks not only an abrupt transition in topography but also a transition in vegetation and agriculture. The poor, thin soils in the unglaciated portion have returned to forest whereas agriculture thrives in the glaciated portion. The highest topographic relief in the state is in far eastern Ohio, in Monroe, Belmont, and Jefferson Counties.