Roger Hux, birder extraordinaire,  told me about 40-Acre Rock Heritage Preserve in Lancaster County. This geological and natural treasure has been protected from development and is open to the public free of charge. SCDNR says that the park is 1, 567 acres and the rock actually 14 acres. It is a National Natural Landmark.  

DIRECTIONS: To get to 40-Acre Rock take route 601 (9 miles) south of Pageland or (11 miles) north of Kershaw. Go west (a left coming from Kershaw) on Taxahaw Road (state route 123) 1.5 miles. Then go left on Nature Reserve road for .4 (4/10) miles and then right on Conservancy Road . It is about 1.5 miles to the rock. You will be able to drive about half way and walk the rest.