The Big South Fork watershed lies within the Cumberland Plateau physiographic province, which is the southern portion of the Appalachian Plateaus structural province. The geology of the National Area is characterized by parallel, horizontally-bedded sedimentary rock of Pennsylvanian age overlaying Mississippian age rock. The Pennsylvanian rocks are predominantly sandstone and shale, and include siltstone, conglomerate, and coal. Oil and gas deposits associated with the Mississippian age limestone are found in many areas within and outside the southern portion of the National Area. There are an estimated 100 abandoned deep coal mine openings and associated spoil piles within the National Area. Mine reclamation efforts, funded by the Office of Surface Mining, have concentrated on areas having visitor access. Approximately 300 active or abandoned oil or gas wells and an unknown number of unmapped wells exist within the National Area. Mineral development is a possibility on the 18,900 acres where previous owners have retained mineral rights, subject to the National Area legislative restrictions and Federal regulations.
The upstream topography of the National Area is characterized by a dendritic drainage pattern and narrow, v-shaped gorges. The focal point of the area is the massive gorge with its many sheer bluffs at the gorge rim towering over wooded talus slopes and the naturally fluctuating river and tributaries below. The valleys are dotted with huge boulders broken from the cliff faces above. Streams include stretches of fast, rugged whitewater and quiet pools. Weathering processes have produced an impressive array of rock formations, including arches, mesas, chimneys, cracks, and rockshelters. Prior to National Area establishment, Tennessee designated Twin Arches and the Honey Creek area as State Natural Areas because of their superlative geological and other natural attributes. The gorge, as defined by the establishing legislation, is roughly one-half of the total acreage of the National Area. The Big South Fork River begins within the National Area at the confluence of the New River with the Clear Fork and flows northward through the National Area for approximately 49 miles. It is free-flowing for about 37 miles until it is affected by the headwaters of Lake Cumberland. Wetlands also have not yet been completely inventoried. Certain National Wetlands Inventory maps have been completed. The Tennessee Wildlife Resources Agency is identifying wetlands over five acres from aerial photography. The Kentucky Division of Water has provided estimates of wetland acreage totaling approximately 530 acres, not including lake-type wetlands associated with Lake Cumberland.