from east to west by the Atlantic coastal plain, the Piedmont, and the Blue Ridge Mountains. Culturally, the coastal plain is split into the Lowcountry and the Pee Dee region. While, the upper Piedmont region is referred to as the Piedmont and the lower Piedmont region is referred to as the Midlands. The area surrounding the Blue Ridge Mountains is known as the Upstate. The Atlantic Coastal Plain makes up two-thirds of the state. Its eastern border is the Sea Islands, a chain of tidal and barrier islands. The border between the lowcountry and the upcountry is defined by the Atlantic Seaboard fall line, which marks the limit of navigable rivers. Atlantic Coastal Plain The Atlantic Coastal plain consists of sediments and sedimentary rocks that range in age from Cretaceous to Present. The terrain is relatively flat and the soil is composed predominantly of sand, silt, and clay. Areas with better drainage make excellent farmland, though some land is swampy. An unusual feature of the coastal plain is a large number of low-relief topographic depressions named Carolina bays. The bays tend to be oval, lining up in a northwest to southeast orientation. The eastern portion of the coastal plain contains many salt marshes and estuaries, as well as natural ports such as Georgetown and Charleston. The natural areas of the coastal plain are part of the Middle Atlantic coastal forests ecoregion. The Sandhills or Carolina Sandhills is a wide region within the Atlantic Coastal Plain province, along the inland margin of this province. The Carolina Sandhills are interpreted as eolian (wind-blown) sand sheets and dunes that were mobilized episodically from approximately 75,000 to 6,000 years ago. Most of the published luminescence ages from the sand are coincident with the last glaciation, a time when the southeastern United States was characterized by colder air temperatures and stronger winds. Piedmont Much of Piedmont consists of Paleozoic metamorphic and igneous rocks, and the landscape has relatively low relief. Due to the changing economics of farming, much of the land is now reforested in loblolly pine for the lumber industry. These forests are part of the Southeastern mixed forests ecoregion. At the southeastern edge of Piedmont is the fall line, where rivers drop to the coastal plain. The fall line was an important early source of water power. Mills built to this resource encouraged the growth of several cities, including the capital, Columbia. The