Appalachia - Topography
The easternmost belt is the Blue Ridge. Composed of ancient Precambrian rocks, this section has been severely eroded, and its highest elevations are currently only a fraction of their former levels. The Piedmont section of the Atlantic southern lowlands bounds the Blue Ridge along Appalachia's eastern side from New York to Alabama.
The Blue Ridge generally increases in elevation and width from north to south. In the south, especially south of Roanoke, Virginia, is the most mountainous part of Appalachia. The changes in elevation from the Piedmont onto the Blue Ridge are usually abrupt and substantial. In Pennsylvania and Virginia, the Blue Ridge is a thin ridge between the Piedmont and the Great Valley to the west; along the North Carolina-Tennessee border, it broadens to a width of nearly 150 kilometers.
To the west of the Blue Ridge, one encounters the ridge and valley section. This is part of the great expanse of sedimentary rock beds that lie between the Blue Ridge and the Rocky Mountains. The eastern edge of these beds has been severely folded and faulted, resulting in a linear topography.
The ridge and valley section averages about 80 kilometers in width. It is occupied by many ridges, usually rising 100 to 200 meters above the separating valleys. Gaps in the ridges are relatively infrequent and usually have been created by rivers that cut across the grain of the area. Several kilometers wide, the valleys provide some of the best farmland in Appalachia. The ridges throughout this section generally are composed of relatively resistant shale and sandstone, and the valleys usually are floored by limestone.
Between the Blue Ridge and the first of the ridges is the Great Valley. Running virtually the entire length of the region, the valley (which is hilly rather than flat in most areas) is historically one of the important routeways in America, and one that has tied the people of Appalachia together more than any other physical feature save the mountains themselves.
The westernmost part of Appalachia is the Appalachian Plateau. The plateau is bounded by a steep scarp (slope) on the east called the Allegheny Front, which was the most significant barrier to western movement in the country east of the Rocky Mountains. The topography of this region has been created largely through stream erosion of the horizontal beds of the interior lowland. Erosion created a rugged, jumbled topography, with narrow stream valleys bordered by steep, sharp ridges. The northern portion of the Allegheny Plateau, in New York and Pennsylvania, has a rounder, gentler appearing landscape. Except for limited areas, level land is scarce. Most communities are forced to squeeze themselves into small level spaces in the stream valleys.
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