GEOLOGY AND BLUE RIDGE ESCARPMENT EVOLUTION ALONG THE TOXAWAY RIVER IN SOUTHWESTERN NORTH CAROLINA

The Blue Ridge Escarpment (BRE), a 500 km-long geologic landform that lies alongside the Eastern Continental Divide, continues to be the focal point of research because of its long history and slow evolution. This research investigates the Toxaway River and its tributary Toxaway Creek in northwestern South Carolina and adjacent southwestern North Carolina in order to understand how the rivers are eroding the escarpment and how they affect Blue Ridge Escarpment evolution. Field studies along the Toxaway River determined the primary bedrock to be Toxaway Gneiss. Thin section analysis performed on Toxaway Gneiss reveals a primary mineralogy of biotite (5-10%), muscovite (10-15%), quartz (20-30%), microcline (20-25%), and plagioclase (20-25%). Where the Toxaway River transects the Brevard Zone, the major rock type is muscovite schist with a mineralogy consisting of plagioclase (15%), quartz (40%), muscovite (40%) with 5% accessory biotite, chlorite, and magnetite. A total of thirty-three joint measurements where collected from bedrock with orientations striking predominantly NS and EW with near vertical dips. Thirty foliation measurements were taken, which strike predominantly to the NE with mainly SE dips. Digital Elevation Model (DEM) analysis gives a watershed of 380 km² and an average gradient of 82.12 m/km. The longitudinal profile of the Toxaway River created from the DEM is generally concave but with two major convexities associated with prominent knickpoints. Knickpoint formation may be the result of rejuvenation of Appalachian topography associated with Late Cenozoic mantle dynamics. The main erosive mechanisms by which the Toxaway River erodes the Blue Ridge Escarpment is through plucking and abrasion. Plucking occurs along orthogonal joints in hard Toxaway gneiss whereas abrasion occurs primarily in areas with softer rocks such as phyllonites and schists associated with the Brevard fault zone. This study corroborates previous studies of other rivers flowing into Lake Jocassee, including the Whitewater, Thompson, and Hosepature Rivers, although all rivers have unique characteristics.