Fall line is a series of waterfalls and rapids formed where hard rock meets softer rock. The falls and rapids develop as erosion by a river or stream wears away some of the softer rock, creating a ledge over which the water flows. In the Eastern United States, a Fall Line stretches from southern New York to Alabama. It formed as water carried away some of the soft sediments of the Atlantic Coastal Plain, leaving behind the harder rocks of the Piedmont--the plateau east of the Appalachian Mountains. Nearly every stream on the Fall Line has rapids or waterfalls.