Fall line
GEOMORPHOLOGIC BREAK THAT DEMARCATES THE BORDER BETWEEN AN UPLAND REGION AND A COASTAL PLAIN
Falls line; Fall-Line; Gnat line; Fall Line; Fall zone; The Fall Line; Fall-line
A fall line (or fall zone) is the area where an upland region and a coastal plain meet and is typically prominent where rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, and the coastal plain is softer sedimentary rock.