The fall line marks the area where an upland region and a coastal plain meet. The fall line is typically prominent where a river crosses it, for there will usually be rapids or waterfalls. Because of these features river boats typically can not travel any further inland. Because of the need of a port, and ready supply of water power, settlements often developed where the river crosses the fall line.

The most prominent example of fall line settlement was the establishment of the cities along the eastern coast of the United States where the Appalachian Rise and the coastal plains meet. Cities on this fall line include: Boston, Massachusetts; Pawtucket, Rhode Island; Troy, New York; Trenton, New Jersey; Washington, D.C; Richmond, Virginia; Raleigh, North Carolina; Columbia, South Carolina; and Augusta, Georgia.