Looking at a satellite image of North America, one's eye is drawn to a swath of parallel ridges and valleys, extending from the lower Hudson Valley of southeast New York to the northern edge of the Coastal Plain, in northeastern Alabama. Sandwiched between the Appalachian Plateau, to its west, and the high spine of the Blue Ridge, to its east, this geophysical province reflects varied Paleozoic sedimentary rocks that accumulated in shallow seas from 500 to 300 million years ago.
As the Continents merged to form Pangea, some 250 million years ago, the Southern Appalachians crumpled upward, lifting the Precambrian core of the Blue Ridge and rippling the Paleozoic strata to its west. Throughout the Mesozoic and Cenozoic Eras (and continuing today), erosional forces have sculpted the landscape, producing ridges of resistant sandstone and valleys of soluble limestone and shale; the largest of the valleys, known as the Great Valley, runs along the east edge of the Province, from central Pennsylvania to northern Virginia, and is renowned for its karst landscape of caves and springs. Many rivers, large and small, were emplaced before the strata of the Ridge & Valley crumpled and lifted; cutting down through the folded and faulted sediments as they rose, these rivers opened water gaps in seams of sandstone, producing the modern illusion that they bore straight through the linear ridges of the Province.
Most highly developed in south-central Pennsylvania, along the Virginia-West Virginia border and in central Tennessee, the Ridge & Valley Province also cuts across northwest Georgia and enters northeast Alabama, fading into the Coastal Plain southwest of Birmingham. The elevation of the ridges is rather modest (generally under 2500 feet) in comparison with the Blue Ridge Mountains to their east and the high wall of the Allegheny Front, to their west. Unlike the crumpled, faulted and overthrust strata of the Ridge & Valley Province, the Paleozoic sediments of the Appalachian Plateau, which stretches from the Poconos of New York to the outskirts of Huntsville, Alabama, are horizontal and undisturbed, broken only by a vast, dendritic network of stream valleys.
