Ridge-and-valley Appalachians

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The Ridge-and-valley Appalachians are a belt within the Appalachian Mountains extending from northern New Jersey westward into Pennsylvania and southward into Maryland, West Virginia, Virginia, and Tennessee. They form a broad arc between the Blue Ridge Mountains and the Appalachian Plateau physiographic province (the Allegheny and Cumberland Plateaus).

The eastern edge of the Ridge and Valley region is marked by the Great Appalachian Valley, which lies just west of the Blue Ridge region. The western side of the Ridge and Valley region is marked by steep escarpments such as the Allegheny Front, the Cumberland Mountains, and Walden Ridge.

These mountains are notable because they form long, even ridges, with long, continuous valleys in between. From a great enough altitude, they look almost like corduroy, except that the widths of the valleys are somewhat variable and ridges sometimes meet in a vee.

These curious formations are the remnants of an ancient fold-and-thrust belt, west of the mountain core that formed in the Alleghenian orogeny(Stanley, 421-2). Here, strata have been folded westward, and forced over massive thrust faults; there is little metamorphism, and no igneous intrusion.(Stanley, 421-2) The ridges represent the edges of the erosion-resistant strata, and the valleys portray the absence of the more erodable strata. Smaller streams have developed their valleys following the lines of the more easily eroded strata. But a few major rivers, such as the Delaware River, the Susquehanna River, and the Potomac River are evidently older than the present mountains, having cut water gaps that are perpendicular to hard strata ridges. The evidence point to a wearing down of the entire region (the original mountains) to a low level with little relief, so that major rivers were flowing in unconsolidated sediments that were unaffected by the underlying rock structure. Then the region was uplifted slowly enough that the rivers were able to maintain their course, cutting through the ridges as they developed.

Valleys may be synclinal valleys or anticlinal valleys.

These mountains are at their highest development in central Pennsylvania, a phenomenon termed the Pennsylvania climax.

[edit] Reference

Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6

[edit] Significant ridges

Name	State
Bays Mountain	Tennessee
Clinch Mountain	Tennessee and Virginia
Sleepy Creek Mountain	West Virginia
North Mountain	Virginia and West Virginia
Powell Mountain	Virginia
Cacapon Mountain	West Virginia
Knobly Mountain	West Virginia
Mill Creek Mountain	West Virginia
Patterson Creek Mountain	West Virginia
South Branch Mountain	West Virginia
Spruce Knob	West Virginia
Sideling Hill	West Virginia, Maryland, and Pennsylvania
Bald Eagle Mountain	Pennsylvania
Nittany Mountain	Pennsylvania
Tussey Mountain	Pennsylvania
Blue Mountain	Pennsylvania
Kittatinny Mountains	New Jersey
Shawangunk Ridge	New York