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Monday, February 13, 2006

Abbreviated Blue Ridge Geology

I received an email today from a young reader asking about the basic geology of this region so I thought I would post this here. As a rule, something like this might be found on another one of my pages, Blue Ridge Reflections. I may go farther in-depth on this subject later and repost it to BRR.

The Blue Ridge is composed of complexly folded and faulted igneous (granitic) and metamorphic rocks. These rocks date to the Precambrian and Paleozoic and represent parts of the basement rock of the North American continent. (See geologic cross-section below.)

When Africa and North America converged during the Paleozoic, these rocks were thrust upward and many miles westward over younger rock materials. Today the general surface of the Blue Ridge lies at about 3000 feet above sea level, with many peaks reaching another 1000 to 2000 feet higher. Elevations increase toward the southwest and culminate in Virginia's two highest peaks, Mt Rogers (5,729') and Whitetop Mt. (5,520'), located near the state's southern border. The Blue Ridge physiographic province is subdivided at Roanoke Gap into two distinct subregions.

Physiographic Subregions of the Blue Ridge

Image above: Blue Ridge geologic cross-section

The area in black is the Blue Ridge Plateau

Blue Ridge Mountains
North of Roanoke Gap, the Blue Ridge occurs as a narrow chain of mountain peaks. Shenandoah National Park lies atop the northern part of the Blue Ridge Mountains. When first set aside in the 1930s, the parkland was deforested and deeply eroded; much of its natural vegetation and wildlife has since been restored to make Shenandoah one of Virginia's main tourist attractions.

Blue Ridge Plateau
South of Roanoke Gap, the Blue Ridge widens into a high plateau. Scattered monadnocks -- A mountain or rocky mass that has resisted erosion and stands isolated in an essentially level area. Also called inselberg.--rise above the general surface level. Mt. Rogers and Whitetop Mt. are on the Blue Ridge Plateau, but geologically, are not part of it. They are composed of volcanic rocks, the origins of which have yet to be fully understood.

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