Topography of the Ridge and Valley Province

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. The boundary between the middle and southern sections is at the divide between the New and Tennessee Rivers. Concerning the middle section, Thornbury (1965) pointed out that the area between the Susquehanna and the James Rivers best illustrates the structure and topography of this province. Here is found the nearest approach to regular repetition of similar folds; the mountain ridges are most numerous and most nearly parallel, and the mountains are the most nearly even-crested and continuous. The Great Valley attains a width exceeding 60 km (Fenneman, 1938).

The topography of the southern section differs in four ways from that of the middle section:

1. Thrust faults are more numerous, and as a result, the regional structure consists largely of strata dipping to the southeast. As a result, homoclinal ridges (i.e., ridges composed of rock layers with similar dips) rather than anticlinal and synclinal ridges are typical;
2. Ridges are not so numerous as in the middle section, and in the latitude of Knoxville, Tennessee, typical Appalachian ridges are practically lacking, so that the entire 60 km between the Great Smoky Mountains and the eastern Cumberland escarpment is essentially the Great Valley type of topography;
3. Because of the sparsity of ridges, no division really exists between a Great Valley to the east and a ridge belt to the west.
4. Longitudinal drainage, in which rivers follow linear nonresistant outcrops for long distances, is more common than it is farther north. Such drainage is well illustrated by the headwater drainage of the Tennessee River. Four streams, the Powell, Clinch, Holston, and Nolichucky-French Broad, form the headwaters of the Tennessee, flowing many kilometers in parallel valleys before joining to form the Tennessee River proper (Fenneman, 1938).

Major streams of the
Appalachian Highlands

From the northern boundary of the southern section, at the New River-Tennessee divide, valley floors broaden and decrease in altitude toward the southwest. Clinch Mountain near the centerline of the province is the one great continuing feature, with all the main ridges north of Knoxville being made by the Clinch or associated features. These include Bays, Clinch, Powell and Wallen mountains. The crests of the higher mountains are predominantly horizontal. These mountains end about 15 km north of Knoxville. From that latitude southward to Georgia, the relief features with only one exception consist of low ridges or knobs held up by rock units of only moderate resistance, such as the Copper Ridge Dolomite and the Rome Formation (Fenneman, 1938).

Extending from east of Chattanooga to near Rome, Georgia, is a belt of mountains called the "Armuchee Ridges" attaining a maximum width of 20 km. This belt owes its existence to a dissected composite syncline. The chief ridgemaker here is the Rockwood, with the Pottsville second in importance. East and west of the ridges the broad lowland is continuous.

East and south of the ridges is the Rome Valley, 20 to 40 km wide, underlain by the Knox dolomite and Cambrian limestones and shales. South of the 34th parallel, in Alabama, the Ridge and Valley province is much more complex in structure and varied in topography. Great thrust faults have brought to the surface the ridge-making formations in the broad belt of Cahawba ridges. The ridge belt is divided longitudinally by the Cahawba Valley, a narrow lowland like those on either side and due to upfaulting of the older, weaker rocks. Crests of considerable continuity are found as far south as Birmingham, Alabama (Fenneman, 1938).

A longitudinal profile of this section based on the general level of hilltops is very flat south of Knoxville and steepens progressively upstream from that point to the New River divide. A similar profile using stream levels shows a slight upturn in passing from the basin of the Tennessee to that of the Coosa. The Tennessee River flows 400 km southeastward in the Ridge and Valley, then turns westward into the Appalachian Plateau.