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 Piedmont and the Allegheny and Cumberland Plateaus.
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.
The curious formation of these mountains is due to the fact that they are the remnants of ancient mountains formed from lateral folding, with relatively little faulting or uplift, and no igneous intrusion. The ridges represent the edges of the erosion-resistant strata, and the valleys portray the absence of the more erodable strata. Valleys may be synclinal valleys or anticlinal valleys.
These mountains are at their highest development in central Pennsylvania, a phenomenon termed the Pennsylvania climax.