Only a very small portion of Virginia extends onto the Appalachian Plateaus, a surface underlain by the same Paleozoic sedimentary rocks as the Valley and Rdige. The difference is that in the Plateaus physiographic province, these rocks have not been deformed and still occur today in horizontal beds. See geologic cross-section. The average elevation of the plateau surface in Virginia is between 2000 and 2500 feet above sea level. Elevations decrease westward across West Virginia, Kentucky and Ohio.
The Appalachian Plateaus are only structurally a plateau. The ancient surface has been eroded by stream action over millions of years into what is today a region of high of relief. Small, narrow valleys (or hollows) twist through the resulting mountains. The older surface is evident in the pattern of hilltops all tending to reach the same elevation. Such an eroded plateau is known as a dissected plateau.
The upturned edge of the Appalachian Plateaus, where the horizontal beds of the plateau give way to the folded beds of the Valley and Ridge, is observable in certain places. This feature is called the Allegheny Front.
Physiographic Subregions of the Appalachian Plateaus
The Appalachian Plateaus are composed of two major plateaus, the Allegheny Plateau and the Cumberland Plateau. This separation has no significance in Virginia's physiography, since all of Virginia that lies in the province is in the Cumberland Plateau subregion. A major distinction between the two plateaus is that the northern Allegheny surface was glaciated during the Pleistocene; the southern Cumberland surface was not. The border between the two lies near the New River in West Virginia.
Created by SLW, January 1997.