Geology

We begin this section on the geology of the Southern Appalachian Mountains with a streamlined description of geologic history by Sandra Clark, retired geologist from the US Geological Survey."The history recorded by humans spans only the past several thousand years on a planet that is 4 1/2 billion years old. Although we know little of earliest times, the history of the last billion years is well recorded in the rocks, much like pages in a book. The record is not one of permanence and stability, but one of continual change. On a scale of millions of years, continents and oceans form and disappear, change in shape and move. Mountains rise out of the sea and later wear down to their roots" (Clark 2002).

Beyond this streamlined description of the geologic history by Sandra Clark, there is much more detail needed to provide a useful understanding for practicing natural resource managers.  It is helpful to examine a geologic time scale in order to understand many of the concepts presented in this geology of the Southern Appalachian Mountains (Table:Geologic Time Scale).

The Appalachian Mountains are the oldest on the continent. Many of their geologic structures were formed more than 200 million years ago during the Paleozoic as the African Continent collided with the North American Continent. This collision compressed, thrust, and folded the North American Continental Plate. Vertical forces pushed up high mountain ranges so that by the end of the Paleozoic these mountains were high and steep and very likely glaciated, perhaps similar to the Swiss Alps today.

During the Mesozoic and Cenozoic, a broad, gentle, vertical crustal uplift predominated,producing folding and thrust falling. As uplift rates decreased, the mountains swiftly began to erode away, so that low mountains replaced the alpine peaks. During these times, erosion of the high mountains poured huge volumes of sediments into the seaways and onto the downwarped crust to the west of the mountains. These sediments now make up the rocks of the Ridge and Valley and the Appalachian Plateau Provinces.

Although glaciation was limited to the Appalachians north of the glacial advance, the Ice Age climate profoundly affected the Appalachian landscape during the Cenozoic. The intense cold associated with the ice age greatly increased the rate of physical weathering processes such as frost wedging.Landforms and deposits, such as sorted patterned ground, are clearly glacial in origin, and much of the hillslope colluvium and talus in the Appalachians probablywere formed inglacial times.

State geological surveys are making available via their Internet sites an increased number of geologic maps, publications, and other geologic information.  New material (e.g. geospatially referenced, digital geologic maps) useful to land managers are being added to these sites periodically, as well as basic geologic information useful for educational and interpretive programs.  Links to these state geological survey sites and to the U.S. Geological Survey site are listed below:

• North Carolina Geological Survey
• Virginia Division of Mineral Resources
• South Carolina Geological Survey
• Tennessee Division of Geology
• U. S. Geological Survey

Note that the Georgia Geological Survey no longer exists.

Although generalized and somewhat outdated in specific areas, a detailed geologic map of the State of North Carolina provides a good overall reference for the distribution of geologic units across the state.