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TheRidge-and-Valley Appalachians, also called theRidge and Valley Province or theValley and Ridge Appalachians, are aphysiographic province of the largerAppalachian Highlands division. The physiographic province is divided into three sections: the Hudson Valley, the Central, and the Tennessee.[1]
The river valleys were areas of indigenous settlements for thousands of years. In the historic period, theCherokee people had towns along many of the rivers in western South Carolina and North Carolina, as well as on the western side of the Appalachian Mountains in present-day Tennessee. Similarly, theCatawba people occupied areas along the upperCatawba River inWestern North Carolina, to the east ofCherokee County.
The ridge and valley system presents an important obstacle to east–westland travel even with today's technology. It was a nearly insurmountable barrier to European-American migrants who walked or rode horsestraveling west to settle theOhio Country, and later theNorthwest Territory andOregon Country. In the era when animal power dominated transportation, there was no safe way to cross east–west in the middle of the range; crossing was only possible nearer its extremes except for a fewrough passages opened mid-range during the colonial era, includingCumberland Gap,Braddock's Road, andForbes Road.
These were later improved as America's first National Roads, includingWilderness Road,Cumberland Road,Lincoln Highway, designated asU.S. Route 40 andU.S. Route 30 in later years. Early settlers ofOhio Country tended to enter it via theOhio River; river systems were the most important transportation corridors. It was difficult in the late 19th and 20th centuries to construct railroads and modern highways through this area.
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The eastern head of the Ridge and Valley region is marked by theGreat Appalachian Valley, which lies just west of theBlue Ridge. The western side of the Ridge and Valley region is marked by steep escarpments such as theAllegheny Front, theCumberland Mountains, andWalden Ridge. The Valley and Ridge is located on the west side of the Blue Ridge Mountains.
The Province extends from southeasternNew York in the north through northwesternNew Jersey, westward intoPennsylvania through theLehigh Valley, and southward intoMaryland,West Virginia,Virginia,Kentucky,Tennessee,Georgia, andAlabama. They form a broad arc between theBlue Ridge Mountains and theAppalachian Plateau physiographic province, which includes theAllegheny andCumberland plateaus. They are characterized by long, evenridges, with long, continuousvalleys in between.
The Valley and Ridge Province was formed during theAlleghanian orogeny, a mountain-building event that occurred between 325 and 260 million years ago.[2] The rocks in the region were subjected to immense pressure and heat, causing them to deform and fold. The softer parts of these rock units (chiefly shale and limestone) were eroded to form the valleys and the harder parts of the folds (quartzites) formed the mountain tops and ridges.[3] The ridges represent the edges of the erosion-resistant strata, and the valleys portray the absence of the moreerodible strata. Smaller streams have developed their valleys following the lines of the more easily eroded strata.[4][5]
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A few major rivers, including theDelaware River, theSusquehanna River, theNew River, and thePotomac River, are older than the present mountains, having cutwater gaps that are perpendicular to hard strata ridges. The evidence points to a wearing down of the entire region to a low level with little relief, so that major rivers were flowing in unconsolidated sediments unaffected by the underlying rock structure. The region was then uplifted slowly enough so that the rivers could maintain their course, cutting through the ridges as they developed.
Valleys in the region are eithersynclinal oranticlinal.
These mountains are at their development in central Pennsylvania, a phenomenon termed the Pennsylvania climax.
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