The Fall Line
October 25, 2017
Photographer: Dale Chadwick
Summary Author: Dale Chadwick
The photo above shows a scenic waterfall on the Towaliga River, in High Falls State Park, Georgia. From Georgia to New England, the fall line along the Atlantic seaboard represents the boundary between the Piedmont and the coastal plain physiographic regions. It's called the Fall Line, for the number of waterfalls and rapids it features along this boundary. The underlying rocks are primarily Paleozoic gneiss and granite in the Piedmont; whereas Cretaceous sedimentary rocks form the base of the coastal plain. The geology of these regions strongly influences their ecology. For example, gnats are often a menace in the coastal plain but are only an occasional nuisance in the higher elevation Piedmont zone. In fact, in some areas of the southeastern U.S., the fall line is referred to as the Gnat Line.
The fall line's geology has also influenced economic history. Rivers were generally navigable below the fall line so towns and cities were established for trade at the point at which a river could be used to transport goods. In addition, the change in altitude between the Piedmont and coastal plain (gneiss and granite are more resistant to erosion than the softer sandstone, shale and limestone underlying the coastal plain) meant that water power (from the flow of falling or fast moving water) could be readily exploited in cities up and down the fall line, including Macon and Augusta, Georgia, Columbia, South Carolina and Richmond and Fredericksburg, Virginia. However, it should be noted that further north, in New England for instance, the coastal plain narrows and the crystalline metamorphic and granitic rocks are very close to the coast. Photo taken on March 11, 2017.