Blue Ridge Province

The Blue Ridge province is divided into two subprovinces, the

Physiographic provinces

Northern Blue Ridge and the Southern Blue Ridge. The Northern Blue Ridge lies north of the Roanoke River and is a narrow range of high mountains that is 395 km long but nowhere exceeds 22 km in width. In its narrowest part it is a single ridge that stands about 365 m above the Great Valley of the Ridge and Valley Province and about 610 m above the Piedmont Lowlands on the east. It is underlain by a sequence of Precambrian and Cambrian rocks that form the northwest limb of the Blue Ridge anticlinorium (Espenshade, 1970). This sequence consists largely of resistant rocks. Only three rock units support the crest of the range: (1) a complex assemblage of medium to coarse granitoid rocks, of which hypersthene granodiorite (Pedlar Formation) is the most resistant; (2) a metavolcanic unit, the Catoctin Formation; and (3) a thick series of quartzite, arkose, and phyllite called the Chilhowee Group, which is early Cambrian in age. The topography of the Northern Blue Ridge is largely due to rock resistance and width of outcrop lithology, howeverthe average altitude of the mountains north of the Potomac River is little more than half that of its southeastern part. Despite similar lithology. This decline may be due simply to less uplift in that region (Hack, 1982).

The remaining discussion in this section willcover only the Southern Blue Ridge Province.

• Topography: The Southern Blue Ridge Province extends from the Roanoke River southwestward into north Georgia.
• Regolith: Although thick saprolite occurs in the Blue Ridge, it generally is not as prominent as in the Piedmont Province, both because it tends to be thinner than in the Piedmont and because surfaces in the Blue Ridge are commonly covered by colluvium.
• Mass Wasting: The most common mass-wasting process in the Blue Ridge is probably downslope movement of colluvium and residuum induced by wind throw of trees.
• Soil: The dominant soil order in the Blue Ridge Province is the Inceptisol. This order consists of relatively young soils that lack horizonswhere illuvial clay has accumulated.
• Streams: Because of the high relief, streams in the Blue Ridge tend to have steep slopes. The erosive power provided by such slopes, together with the presence of generally hard bedrock, have produced many gorges.