A NEW REGIONAL COMPILATION OF TWELVE 7.5-MINUTE GEOLOGIC QUADRANGLE MAPS, INNER PIEDMONT OF SOUTH CAROLINA AND ADJACENT NORTH CAROLINA: THE MOUNTAIN BRIDGE AREA AND BEYOND

A compilation of recent geologic mapping covers a large portion of the Blue Ridge Front, between Highway 130, Oconee County, and Highway 25, Greenville County, South Carolina, as well as parts of adjacent North Carolina The mapping was conducted at 1:24,000 scale and covered twelve 7.5-minute quadrangles. The Mountain Bridge area is included in the compilation. Most of the geologic information portrayed has GPS control. Staff and students of Furman University began the mapping in 1995 and were assisted later by personnel of the SCDNR-Geological Survey.

The geology mapped is in the western Inner Piedmont. The regional structural grain is northeast. Map patterns, however, are defined locally by Type III superimposed folds verging northwest and southwest. Major structural elements are, west to east: the east flank of the Toxaway Dome, the Rosman fault, the Brevard Zone, and three major vertically stacked, allochthonous rock packages. These packages are the Jocassee thrust sheet, the Walhalla nappe, and the Six Mile thrust sheet. The Jocassee thrust sheet consists primarily of Henderson Gneiss and is separated from the overlying Walhalla nappe by the ductile Eastatoee thrust. Rocks of the Walhalla nappe were folded and overturned subsequent to thrust emplacement. Schist-metagraywackes of the Chauga River Formation and overlying epidote-amphibolite-grade Poor Mountain Formation crop out near the base. Table Rock gneiss overlies those rock units, locally separated from them by fault or intrusive contacts. Poor Mountain amphibolite and associated ultramafic rocks also are complexly folded within the main body of Table Rock gneiss. The structurally highest Six Mile thrust sheet overlies the Walhalla nappe, and the ductile Seneca thrust separates the two. Six Mile rocks contain kyanite- and sillimanite-grade gneisses, schists, and amphibolites of the Tallulah Falls and Poor Mountain Formations. Like those in the Walhalla nappe, Six Mile rocks were folded and overturned subsequent to Seneca emplacement. Brittle thrusts postdate and locally duplicate the ductile ones. Post-Paleozoic brittle faults of easterly and northeast trends displace and disrupt the aerial continuity of the different thrust sheets. The faults are part of the Marietta-Tryon fault system.