In the Atlantic coast of the U.S, especially in the South, the area between the Tidewater coastal plain and the actual Appalachian Mountains. The line between the coastal plain and the Piedmont is the fall line where waterfalls or shoals block navigation upriver from the coast. This area was still a frontier while the coastal plain was quite well settled, and sectional conflicts existed between the coastal areas (site of the majority of Southern plantations) and the smaller farmers moving into the Piedmont.