Fall Line

Fall Line, boundary between an upland region and a coastal plain. At a fall line, streams flowing out of an upland region descend over rapids or waterfalls to the softer, and less rocky, soils of a coastal plain. In the eastern United States, for instance, a fall line forms the border between the Piedmont Plateau and the Atlantic Coastal Plain. Because it marks the head of navigation on rivers and because the falls furnish water-power, this fall line is the site of many cities, including Philadelphia, Baltimore, and Washington, D.C. Other notable fall lines include the Brahmaputra near Dibrugarh, India, and the Danube near Budapest, Hungary.