Ridge and Valley Province

Physiographic provinces

The Ridge and Valley Province extends from north-central Alabama to beyond the late-Wisconsinan glacial border in Pennsylvania. It is underlain by Paleozoic sedimentary rocks that have been folded and thrust from the southeast. Tight folds characterize the northern part of the province, whereas stacking of thrust sheets characterizes the southern part. The southeastern border of the province is a broad, linear lowland called the Great Valley, but most of the Province consists of alternating ridges and valleys. Elevations generally range from 300 to 900 m, although extremes are 120 to 1,300 m (Fenneman, 1938).

Geologic Cross Section

Effect of Structure on Topography

The contrast in bedrock resistance to erosion is greater in the Ridge and Valley than in any other province. Some sandstone and conglomerate units, for example,are many times more resistant than the abundant shale and carbonate rocks. Because of this variation, differential erosion, in which resistant rocks come to form ridges and mountain peaks while easily eroded rocks form valleys, is very prominent in shaping the landscape. Thus, lithology and structure are more dominant in determining the topography than in other provinces. Certain resistant units repeat themselves and are widespread ridge makers. To the north these include the Pottsville Sandstone of Pennsylvanian age, the Pocono Sandstone of Mississippian age, and the Tuscarora Sandstone of Silurian age. To the south, such units include the Pottsville, the MississippianFort Payne chert, and the Silurian Clinch (equivalent to the Tuscarora).

Effect of Structure and Rock Type

• Topography: Traditionally the Ridge and Valley Province is divided into three sections, of which the southern part of the middle section and the southern section are of concern here.
• Regolith: The most common transported regolith associated with highlands in the Ridge and Valley Province is what will be termed "boulder colluvium".
• Soil: A strong difference exists between soils formed on carbonate-rich rocks in valleys and those developed on siliciclastic rocks on ridges.
• Mass Wasting: The colluvium on sandstone-capped ridges is coarse, like that in the Blue Ridge, and so debris slides and flows are more common than types of mass wasting associated with fine-grained debris.
• Karst Landscape: The Ridge and Valley, particularly the Great Valley, is one of the major karst regions of the United States. Many famous commercial caverns, such as Luray, Shenandoah, and Endless, occur in the Shenandoah Valley of Virginia.
• Streams: Several streams rise near the crest of the Blue Ridge and flow northwesterly across this province. Generally, however, when they reach the Ridge and Valley Province they turn southwesterly and flow along strike valleys parallel to the general Appalachian trend. The French Broad River is an example.