The Upstate region contains the roots of an ancient, eroded mountain chain. It is generally hilly, with thin, stony clay soils, and contains few areas suitable for farming. Much of the Piedmont was once farmed. 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 the 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 harness this resource encouraged the growth of several cities, including the capital, Columbia. The larger rivers are navigable up to the fall line, providing a trade route for mill towns.