The geologic heritage of the Blue Ridge in particular and the Southern Appalachians in general is one of the most fascinating subjects one can explore. I often give a presentation called “Where Are We?” at the onset of my natural history workshops. This allows me to touch upon the basics of the region’s geologic and physiographic formation and thereby lay the groundwork for subsequent field trips in which the distinctive habitats, plants (especially wildflowers) and animals (especially birds) are identified. “Where Are We?” goes something like this.

The Appalachians — created between 300 and 250 million years ago as a result of periods of mountain building brought about when the North American continental plate collided with the plates forming the European and African continents — extend some 2,000 miles from Canada’s Gaspe Peninsula to north Georgia and Alabama. It was during this period, of course, that the massive super continent now known as Pangea was formed.

How high were the Appalachians when first uplifted as a young and bare mountain range? No one knows for sure, but they were probably higher than the Rockies are today and perhaps not as high as the present-day Himalayas. A height of about 22,000 feet is probably in the ballpark. They have, of course, eroded down into the mature ranges we can explore today that are so rich and diverse in regard to distinctive habitats and plant species.

Some geologists, like David Prowell of the U.S. Geologic Survey in Atlanta, are now beginning to consider the possibility that the original Appalachians eroded “down to nothing long ago, and that the current terrain was formed 140 million years ago as a westward crawl of a continental plate that continues to nudge the mountains upward.” Normally, mountains tend to weather away to nothing within 50 million years, regardless of height. Prowell “estimates that the growth (of the Southern Appalachians, especially the Blue Ridge) is slight — about 100 feet every million years or so — but enough to offset erosion.” (Prowell presented these ideas last March at the Geologic Society of America’s Southeastern section meeting in Charleston, South Carolina.)

Even without the involvement of Prowell’s westward-crawling continental plate, geologists have contended for years that as mountains erode downward they also — paradoxically enough — rise upward. Rock is less dense than material lower in the mantle. When mighty mountain ranges are uplifted, the underlying layer is depressed. A “root” develops that helps “buoy up” the less dense mountains. As the mountains erode the pressure is decreased so that simultaneous uplift also occurs. The technical term for this is “isostatic rebound.” (See “A Geologic Adventure Along the Blue Ridge Parkway in North Carolina,” Bulletin 98, NC Geologic Survey Section, Raleigh NC, 1999, p. 7.)

It’s probable that numerous factors in addition to erosion, isostatic uplift and ongoing plate action are also involved. It is out of this sort of complexity that the wondrous mountains we call home are created anew each day.

I define the Southern Appalachians as those mountains south of the point in northeastern Pennsylvania to which glacial ice sheets extended at the height of the Wisconsin glacial epoch 18,000 years ago. This unglaciated region consists of four distinct geographic provinces: Piedmont, Blue Ridge, Ridge and Valley, and Cumberland Plateau.

The piedmont region to the east of us here in Western North Carolina is the eroded eastern rim of the ancient Southern Appalachians. Foothill peaks and ranges like Pilot mountain and the Uwharries are piedmont remnants of what was once much higher terrain. Some geologists do not consider the Cumberland Plateau to be a part of the Southern Appalachians because it was actually a part of ancient North America that predated Appalachian uplift. But the region was so deformed by the cataclysmic events of 250 million years ago that I see no way in which it can be excluded from the Southern Appalachians.

In regard to mountainous terrain the Blue Ridge Province is by far the most significant region in eastern North America. The province extends from just south of Harrisburg, Pa., to the hills of north Georgia just north of Atlanta, encompassing the mountainous portions of central Maryland, southwestern Virginia, western North Carolina, east Tennessee, northwest South Carolina, and north Georgia.
Geologists further subdivide the Blue Ridge into northern and southern provinces, with the Southern Blue Ridge Province (SBRP) consisting of the mountainous terrain south of Mt. Rogers in southwest Virginia to Mt. Oglethorpe in Georgia just north of Atlanta.

The eastern front or escarpment of the SBRP is clearly defined from Virginia into South Carolina. (It is this eastern front when seen from the distance as a continuous blue line of mountains that gives the province its name.) On its western front the SBRP consists of the Unaka, Great Smoky, Unocoi and other massive ranges. Connecting the eastern and western fronts are numerous transverse mountain ranges like the Blacks, Great Craggies, Great Balsams and Nantahalas. As a whole, the Appalachian system as a whole reaches its greatest elevation, largest mass and most rugged topography in the SBRP where 82 peaks rise 5,000 feet or more, with 40 or so of them surpassing 6,000 feet in elevation. (Keep in mind the fact that from the North Carolina-Virginia state line northward in the Appalachians to the Gaspe Penninsula in Canada only Mt. Washington in New Hampshire exceeds 6,000 feet.)

This topography profoundly influences the region’s average temperature (and thereby its plant and animal life, which exhibit strong northern affinities), since for each 1,000 feet gained in elevation the mean temperature decreases about 4 degrees F, equivalent to a change of from 200 to 250 miles in latitude. (This means that if you travel from the lowest elevations in the SBRP at about 1,500 feet to the higher elevations above 6,000 feet, it’s like traveling more than 1,200 miles northward in regard to the habitats you will encounter.)

The SBRP is situated where winds bringing saturated air masses from the Gulf of Mexico and the southern Coastal Plain are cooled and lose much of their content. (Warm air cools while rising to pass over a mountain range and can hold less moisture than warm air; therefore, heavy condensation occurs where large fronts first encounter massive ranges, as is the instance along the Blue Ridge divide.) The heaviest rainfall in the entire Appalachian region occurs along the Georgia-South Carolina-North Carolina borders, resulting in annual rainfalls of over 90 inches in many areas. (As much as 145 inches have been recorded since 1935 in certain spots by the Coweeta Hydrologic Lab, which is located near Otto in Macon County just north of the Georgia state line.) Taking this into consideration, some observers now refer to the area as a “temperate” or “Appalachian” rain forest.

The higher elevations of the SBRP, above, say, 4,000 feet, can be thought of as peninsula of northern terrain extending into the southeastern United States, where typical flora and fauna of northeastern and southeastern North America flourish. The region features approximately 1,500 vascular plants (many of which are considered to be showy wildflowers) and 125 species of trees (in all of Europe there are only about 75 species of trees).

So, when those of you who reside in WNC wake up each morning and ask yourself “Where Am I?” simply say to yourself: “I’m in the general area of the Great Smokies, a large mountain range situated on the western front of the SBRP; indeed, it’s the largest single mountain range in eastern North America.”
Even so, the Great Smokies’ range is only one of the numerous units that make up the SBRP, which is, in turn, a part of the Blue Ridge Province, one of the four provinces in the Southern Appalachians that are a part of the Appalachian mountains in eastern North America in the western hemisphere of this sweet planet Earth.” Then you can say “Thank goodness” - because you know where you are - and roll over and go back to sleep.

(George Ellison is a writer who lives in Bryson City. He wrote the biographical introductions for the reissues of two Appalachian classics: Horace Kephart’s Our Southern Highlanders and James Mooney’s History, Myths, and Sacred Formulas of the Cherokees. Readers can contact him at P.O. Box 1262, Bryson City, N.C., 287713, or at ellisongeorge@cs.com

 

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