The Columbus to Augusta. As the Mesozoic shoreline of the Atlantic Ocean, it separates Upper Coastal Plain sedimentary rocks to the south from Piedmont crystalline rocks to the north. The fall line is notable not only for the geological relationship but also for the impact that the geology had on early transportation and consequently on commerce and society.
The falls that give rise to the term fall line are the shoals or waterfalls caused by the first exposure of crystalline rocks encountered when traveling upstream in rivers of the Coastal Plain. These falls represent a barrier to navigation.
Rivers of the Coastal Plain were a major means of commercial transportation during the 1700s and early 1800s. The cities of Columbus, Macon, Milledgeville, and Augusta were located at the fall lines of the Chattahoochee, Ocmulgee, Oconee, and Savannah rivers, respectively. They became early centers of commerce because of their positions at the upstream limit of navigation.
The differences in geology to the north and south of the fall line give rise to differences in soil types, hydrology, and stream morphology. Sandy soils predominate to the south of the fall line, whereas clay soils are the rule to the north. Wide floodplains have developed along many of the streams south of the fall line. Narrower stream valleys are present north of the fall line. A consequence of these differences is that the fall line separates significantly different plant and animal communities.