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What is the fall line between the Piedmont and the Atlantic Coastal Plain?
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Appalachian Mountains
Blue Ridge, part of the Appalachian Mountains.
The fall line is a geographic zone, approximately 30 miles (50 km) wide, that serves as the boundary between the Piedmont and the Atlantic Coastal Plain in the eastern United States.12
This transition zone is characterized by the descent of rivers from the higher, more resistant metamorphic rocks of the Piedmont to the lower, softer sedimentary rocks of the coastal plain. As these rivers cross this boundary, they form numerous waterfalls and rapids.13
Because these features interrupt river travel, the fall line historically marks the inland limit of navigation for ships coming from the coast. Consequently, many major cities were established along this line, including Trenton, Philadelphia, Baltimore, Washington, Richmond, and Augusta.14