GEOLOGY AND EVOLUTION OF THE BLUE RIDGE ESCARPMENT ALONG THE HORSEPASTURE RIVER IN NORTHWESTERN SOUTH CAROLINA AND ADJACENT NORTH CAROLINA

The Blue Ridge Escarpment (BRE), a 500 km long geologic landform lying alongside the Eastern Continental Divide, continues to be the focus of study because of its long history and slow evolution. This research investigates the Horsepasture River in northwestern South Carolina and adjacent southwestern North Carolina to determine how the river is eroding and thus how it affects the Blue Ridge Escarpment evolution. Field studies along the Horsepasture River determined the dominant bedrock to be Toxaway Gneiss. Thin section analysis performed on 7 rock samples showed the primary mineralogy consists of microcline (35-40%), plagioclase (15-20%), quartz (20-30%), and biotite (10-15%), with accessory muscovite, epidote, myrmekite, and titanite. Whole rock chemistry reveals a relatively consistent range of silica content from 70.25% to 73.66% weight percent SiO₂, corresponding to the abundance of quartz seen in thin section. Water samples collected from the 4 rivers that flow into Lake Jocassee contain dissolved silica with the Horsepasture River containing the greatest amount, 95.65 mmol/L. A total of 24 joint measurements were collected in bedrock with orientations striking dominantly NS and EW with near vertical dips. A total of 17 foliation measurements were collected in the Toxaway Gneiss having orientations dominantly striking NE with both NW and SE dips. A Digital Elevation Model (DEM) analysis reveals a watershed of 235.10 km²and a gradual decrease in gradient along the Horsepasture River. A longitudinal profile of the river extracted from the DEM is concave, with low gradient in between prominent knickpoints, which are noticeably convex. It was determined that the Horsepasture River is eroding into the Blue Ridge Escarpment primarily through plucking along orthogonal joint surfaces, creating two prominent knickpoints. Abrasive mechanisms are also responsible for erosion as evidenced by potholes and stream-abraded bedrock. Knickpoint formation appears to be the result of rejuvenation of Appalachian topography associated with Lake Cenozoic mantle dynamics.