Sandhills

The Sandhills are gently rolling hills that form the uppermost portion of the coastal plain in South Carolina. They continue beyond South Carolina westward into Georgia and northward into Virginia. The Sandhills are composed of discontinuous bands of clay and sand that cut the state diagonally in a northeast to southwest direction, forming approximately twelve percent of the state. The Sandhills lie within many counties, including Richland and Lexington (which form the Columbia metropolitan area), Aiken, Barnwell, Kershaw, Chesterfield, and portions of Bamburg, Orangeburg, Sumter, Lancaster, Marlboro, and Darlington. There are many elevated locations throughout the Sandhills from which to view the rolling terrain, especially along ridges in northeastern Columbia, Edmund in the high dunes in Lexington County, Manchester State Forest in Sumter County, and McBee and Sand Hills State Forest in Chesterfield County.

The name “Sandhills” can be misleading, for the sediments that compose the region include tremendous amounts of clay as well as sand. The underlying geology of the Sandhills begins in some areas with Cretaceous clays that form the lowest visible layers. They are well exposed in sites throughout the region that have been cut by streams and rivers. These clays often have a maroon and pink, mottled color. Where thick beds of Cretaceous clays are accessible, as in Aiken County, they are often mined. In other portions of the Sandhills the sediments sit directly atop Piedmont rocks, where because the Cretaceous had previously eroded away, they form unconformites. Within the Sandhills many other clay and sand formations of interest to the geologist and hobbyist are found. Some interesting locations include sediments of Paleocene age found in eastern Richland County near Fort Jackson and the sandstones and varieties of sand found at Peachtree Rock in Lexington County near Edmund.

The clay and sands of the Sandhills came from the Blue Ridge and Piedmont Mountains that stood to the north and northwest. The sand was derived primarily from granites, gneisses, and schists, rocks that formed the cores of these mountains. Because the chemical weathering process altered the micas and feldspars in these rocks to clay that then leached out of the rock, over millions of years the more stable and harder quartz was freed to become sand. These sands and clays were then carried downstream to the coast, which, due to the rising and falling of the sea, was then located in what is now the middle of South Carolina. The currents of the sea worked and shaped the sands into ridges, and winds blew the sand into dunes. Some of these dunes are mined for their relatively pure silica content, particularly in Lexington County. As water moved through the sand, it carried minerals in solution, including silica and iron that helped to cement sand to form sandstones. Remnants of these sandstones are not common in the Sandhills but can be seen in a few sites, including Sugarloaf Mountain. A large amount of the clays that were also brought downstream by rivers was deposited with the sand to form the Sandhills. These clays and sands eroded further as the sea regressed and exposed the surface to more recent erosion. The geology of the Sandhills, then, is primarily a story of rising and falling sea levels, of erosion and deposition.

The geology of the Sandhills has shaped the use of the land. Quartz sand (SiO2), abundant in the Sandhills, contains few nutrients, and the consequent absence of organic matter in the soil causes great permeability. Therefore, rainwater drains rapidly through the sandy soil, further leaching it and leaving a relatively acidic, infertile topsoil. In addition, the clays often bake into hardpans in which plants have difficulty growing. As a result, the Sandhills support a tenacious and in places desertlike, or xerophytic, plant life that includes scrub turkey oak, longleaf pine, briars, berries, and cactus. The Carolina Sandhills National Wildlife Refuge in Chesterfield County provides examples of relatively undisturbed and mature Sandhills ecosystems. These poor growing conditions led farmers in the eighteenth and early nineteenth centuries to avoid the Sandhills. Some crops, however, were found to do well in the sandy soils. Peaches are grown in many parts of the Sandhills, including Saluda, Edgefield, and Lexington Counties, and small truck farms are common.

The Sandhills overlap both the hard rock of the Piedmont and the sediments of the upper coastal plain. As rivers cut through the Piedmont rock and meet the coastal-plain sediments, they form a fall zone that is up to a mile and a half wide in places. The sharp differences in elevation between rock and sediment at the fall zone produce river rapids, which were key to the social and economic development of South Carolina. The fall-zone rapids provided energy that powered mills that facilitated industrial growth. The rapids of the fall zone also created a barrier to inland navigation, and many of South Carolina’s significant inland towns were located at these heads of navigation, including Columbia, Hamburg (North Augusta), Camden, and Cheraw.

Kovacik, Charles F., and John J. Winberry. South Carolina: The Making of a Landscape. 1987. Reprint, Columbia: University of South Carolina Press, 1989.

Murphy, Carolyn H. Carolina Rocks! The Geology of South Carolina. Orangeburg, S.C.: Sandlapper, 1995.