Approximately 2,200 miles in length, the Atlantic Coastal plain stretches from Cape Cod, Massachusetts, all the way to the southern tip of Florida. The western border of the coastal plain, known as the fall line, separates it from the Piedmont region. Many major cities in the eastern United States were built on the coastal plain such as Boston, New York, Washington, and Miami. Much of the coastal plain is covered by marshes and swamps.