Generally refered to as the Carolina
Sand Hills, this is a geographic/geologic region extending from Georgia
to southern Virginia
along the boundary between the piedmont
and coastal plain
. The Sand Hills are one of the dominant features of the Midlands
of South Carolina
but the Midlands include parts of the upper coastal plain and lower peidmont.
The Sand Hills are just that. The local soil (if you can call it that) composed almost entirely of coarse quartz sand, loosely consolidated, which drains water very quickly. This lends the area a dry feel, despite having fairly high rainfall. Although it has been farmed extensively, the area is largely returning to pine-and-scrub-oak forests, often with fairly large (several square meters) patches of bare sand which add to the bleak feel of the area.
The most common explanation for the origins of the Sand Hills is that they are leftover beaches from the when higher sea-levels had the coast at this point. However, the sand grains do not contain ground shells or other beach remnants, and since they sit immediately atop and are surrounded by Cretaceous sediments (~ 146 - 65 million years ago, or mya), this seems unlikely. Although the exact chronology is not known, the best estimate for the time of their formation is around the Eocene (~ 45 mya) or Oligocene epoch (~ 30 mya), although this is debated. The current prevailing geologic theory for their formation is aeolian sand dunes formed in a desert caused by the rain shadow of the (then somewhat taller) Appalachian Mountains, somewhat like the Great Sand Dunes of Colorado.
The Sand Hills region is somewhat seismically active (by east coast standards], although not as active as the Charleston area of the coastal plain.
In western Nebraska there is also a large area known as the Nebraska Sand Hills. This is, by most accounts, a large Pleistocene dune feild. With the retreat of the last ice age, high plains vegetation has stabilized these dune feilds. This is a common feature in the western great plains, with similar examples at least as far south as the Texas panhandle. The Nebraska Sand Hills are, to my limited knowlege the largest such stabilized dune feild in the lower 48.
Many thanks to my geology prof, Terry Ferguson, at Wofford College