The Big South Fork watershed lies within the Cumberland Plateau, which is in the southern portion of the Appalachian Plateaus structural province. The geology of the Big South Fork is characterized by parallel, horizontally-bedded sedimentary rock of Pennsylvanian and Mississippian age rock. The Pennsylvanian rocks are predominantly sandstone and shale, and include siltstone, conglomerate, and coal.  The weathering processes on these rocks have produced an impressive array of formations, including arches, mesas, chimneys, cracks, and rockshelters.  The underlying Mississippian age limestone contains oil and gas deposits which are found both within and outside the Big South Fork.

The stream topography of the area is characterized by a dendritic drainage pattern and narrow, v-shaped gorges.  A focal point of the area is the Big South Fork River gorge with its many sheer bluffs at the gorge rim towering over wooded talus slopes. The river valleys of the area are dotted with huge boulders which have broken from the cliff faces.  The park’s rivers and streams are characterized by stretches of fast, rugged whitewater and quiet pools.