The often stunningly beautiful, broad beaches of Georgia and South Carolina are almost all situated on barrier islands, long islands parallel to the shoreline and separated from the mainland by a sheltered body of water. Because they’re formed by the deposit of sediment by offshore currents, they change shape over the years, with the general pattern of deposit going from north to south (i.e., the northern end will begin eroding first).

Most of the barrier islands are geologically quite young, only being formed within the last 25,000 years or so.

Natural erosion, by current and by storm, combined with the accelerating effects of dredging for local port activity has quickened the decline of many barrier islands. Many beaches in the area are subject to a mitigation of erosion called beach renourishment, which generally involves redistributing dredged material closely offshore so that it will wash up on and around the beach.

As the name indicates, barrier islands are another of nature’s safeguards against hurricane damage. Historically, the barrier islands have borne the vast bulk of the damage done by hurricanes in the region. Tybee Island near Savannah was completely under water in the hurricane of 1898. More recently, Sullivan’s Island near Charleston was submerged by Hurricane Hugo. Like the marshes, barrier islands also help protect the mainland by absorbing the brunt of the storm’s wind and surging water.

Though barrier islands are ephemeral by nature, they have played an important role in the area’s geography from the beginning of time. In fact, nearly every major settlement on the Georgia coast today—including Savannah, Darien, and Brunswick—is built on the vestiges of massive barrier islands that once guarded a primordial shoreline many miles inland from the present one.

By far the largest of these ancient barrier islands, now on dry land, is the fabled Trail Ridge, which runs from Jesup, Georgia, to Starke, Florida. The Trail Ridge’s height all along its distance made it a favorite route first for Native Americans and then for railroads, which still run along its crest today.

The Trail Ridge is such a dominant geographical feature even today that it’s actually responsible for the formation of the Okefenokee Swamp. The Ridge effectively acts as a levee on the swamp’s eastern side, preventing its drainage to the sea.