The Coastal Plain, a region low in elevation, generally consists of a surface gently sloping toward the ocean. It can be divided into an Inner Coastal Plain and an Outer Coastal Plain. Including almost two thirds of the state, the Coastal Plain is South Carolina's largest landform region. The counties generally identified with the Coastal Plain are Marlboro, Darlington, Sumter, Barnwell, Bamberg, Orangeburg, Calhoun, Florence, Marion, Dillon, Horry, Georgetown, Williamsburg, Berkeley, Clarendon, Charleston, Dorchester, Colleton, Hampton, Allendale, Jasper, and Beaufort. The Pee Dee, the area drained by the Pee Dee River System, is a sub region of the Coastal Plain.