SCSouth Carolina Geography

A beach a hundred miles from the ocean

Drive into Columbia, Camden or Aiken and the soil turns to deep white sand. It is a beach. The Sandhills are a fossil shoreline, the dunes of an Atlantic that once stood far inland when sea level was much higher, and they run as a belt across the middle of South Carolina. Their inner edge is the Fall Line, where the hard crystalline rock of the Piedmont gives way to soft coastal sediment and every river drops over rapids.

That geological seam decided where the capital went. Boats coming up from Charleston could get no further than the rapids, so in 1786 the legislature planted a new capital precisely there, at the point where the Broad and the Saluda join to form the Congaree. Columbia is a Fall Line city in the same sense as Augusta, Raleigh and Richmond, and the line strings them together in a diagonal arc down the seaboard.

Mountains to barrier islands in 250 miles

South Carolina is a rough triangle roughly 260 miles across, and it fits an entire cross-section of the southeast into that span.

Belt	Share of the state	Character
Blue Ridge	About 2 percent	Steep, very wet, 3,553 feet at the top
Piedmont	Roughly a third	Rolling red clay over old crystalline rock
Sandhills	A narrow belt	Ancient dunes, sandy and droughty
Coastal Plain	Most of the remainder	Flat, blackwater rivers, bottomland forest
Coastal Zone	The outer rim	Salt marsh, tidal creeks, barrier islands

Sassafras Mountain, 3,553 feet, is the high point, and it straddles the North Carolina line in Pickens County. An observation deck opened on the summit in 2019 with the state boundary running across the platform. Just below the peaks the Blue Ridge Escarpment drops away in a wall that people there call the Blue Wall, and because it forces damp air straight upward the Jocassee Gorges beneath it catch 80 inches of rain or more in a year, some of the wettest ground in the eastern United States. Waterfalls are everywhere in that corner, Raven Cliff Falls dropping around 400 feet.

The Carolina bays

Scattered across the Coastal Plain are thousands of shallow elliptical depressions, most of them holding wetland or peat and many long since drained for farmland. What makes them strange is that they all point the same way. Their long axes run northwest to southeast, and each one carries a sand rim on its southeastern end. They range from a couple of hundred feet across to several miles long. Nobody has settled how they formed; wind and wave action on an ancient high water table is the leading explanation, and a meteor origin has been argued and largely abandoned. Woods Bay State Park near Olanta preserves one that was never drained.

Rivers rerouted, and a harbor that filled with mud

Four systems drain the state. The Savannah forms the entire Georgia border and rises in the Chattooga, which was given federal Wild and Scenic protection in 1974. The Santee is the largest. The Pee Dee comes down through the northeast. The Edisto is often described as the longest free-flowing blackwater river in North America; blackwater rivers take their tea color from tannins leaching out of swamp vegetation rather than from suspended silt.

The Santee is the one that got rebuilt. Between 1939 and 1942 the Santee Cooper project dammed it into Lake Marion and Lake Moultrie, roughly 110,000 acres of new water, and pushed most of the Santee's flow across into the much smaller Cooper River to turn hydroelectric turbines. The unintended result was that all the sediment the Santee had been delivering to the open coast now went into Charleston Harbor instead, which silted so badly that dredging became ruinous. In 1985 the Army Corps of Engineers finished a rediversion canal near St. Stephen that sends about 80 percent of the water back to the Santee, and the harbor stopped filling.

Downstream of Columbia, Congaree National Park protects the largest surviving stand of old-growth bottomland hardwood forest in the southeast. It is a floodplain rather than a swamp, and the regular flooding fed some of the tallest trees in eastern North America.

The border that moved in 2017

The 334-mile line between North and South Carolina was first run in the eighteenth century by surveyors who got parts of it wrong and whose markers later rotted or disappeared. A joint commission spent twenty years relocating the original line with modern instruments, and the corrected boundary took legal effect on 1 January 2017. Around 1,400 parcels were touched, 19 houses changed states outright, and 54 more properties ended up split between the two. The odd stair-step in the line southwest of Charlotte is a genuine surveying artifact, not a design.

One very large earthquake and one very large surge

South Carolina is not thought of as earthquake country, but on 31 August 1886 a shock estimated between magnitude 6.9 and 7.3 struck near Charleston, wrecked much of the city and was felt as far away as Boston and Chicago. It pushed up sand blows across the Coastal Plain that geologists still map today.

Hurricane Hugo came ashore at Sullivan's Island just after midnight on 22 September 1989 as a category four storm and drove a surge of about 20 feet into Bulls Bay, the highest ever measured on the United States east coast. The state's temperature records are 113 degrees, set at Columbia and Johnston on 29 June 2012, and 19 below zero at Caesars Head on 21 January 1985. All of South Carolina keeps Eastern Time.

Common questions

Geography of nearby southern states

More about South Carolina