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The Valley and Ridge province has developed on thick, folded beds of sedimentary rock deposited during the Paleozoic. The long axes of the folded control the shapes and orientations of a series of long, narrow parallel ridges and intervening valleys. The differing degrees of resistance to erosion of the sandstones, shales, and carbonate rocks comprising the lithology determine local relief. In general, the more resistant sandstones cap the ridgetops, protecting softer bedrock below from erosion; limestones and other carbonate rocks form the lowlands and valleys.
The Valley and Ridge is subdivided into two subregions, the Valley of Virginia and the Allegheny Mountains.
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Valley of Virginia |
Allegheny Mountains |
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The Valley of Virginia can itself be subdivided into a string of river basins. From northeast to southwest, one encounters the Shenandoah Valley, the James River Valley, The Roanoke Valley, the New River Valley, and the Holston Valley. Elevations vary from basin to basin. The highest divide occurs near Rural Retreat in Wythe County; waters flowing north to the New River or south to the Holston system separate at about 2400 feet above sea level. The valley floor slopes in both directions away from the New/Holston divide. The Holston leaves Virginia at an elevation of about 1400'; the Shenandoah crosses Virginia's northern boundary at about 400 feet above sea level.
Throughout the Valley of Virginia, hills and ridges rise above the general elevation of the valley floor. Massanutten Mt., a 50-mile long folded mountain in the middle of the Shenandoah Valley section, attains an elevation slightly higher than 2000 feet above sea level.