This is a satellite image of Georgia, with county lines superposed in black. In red are shown the principal geologic provinces of the state. To the northwest is the Valley and Ridge (VR) province of folded and faulted Paleozoic sedimentary rocks. To the east of the Valley and Ridge is the southern end of the Blue Ridge (BR), which consists mostly of Precambrian and Paleozoic metamorphic rocks. Southeast of it is the Piedmont, a hilly or rolling region of Precambrian and Paleozoic igneous and high-grade metamorphic rocks. In the southeast half of the state is the Coastal Plain, a region of undeformed and thus nearly flat-lying Cretaceous and Cenozoic sedimentary rocks and sediments.
The boundary between the Piedmont and Coastal Plain is the Fall Line. It's called the Fall Line because the first falls or rapids in rivers that one encounters as one comes inland from the ocean are usally found at this boundary, as the streams drop off the Piedmont and onto the Coastal Plain. In Georgia, the cities of Columbus (C), Macon (M) Milledgeville (M) and Augusta (A) developed on the Chattahoochee, Ocmulgee, Oconee and Savannah Rivers where inland shipping was stopped by falls or rapids at the Fall Line. Columbia, SC, is a similar Fall Line city. One can see from the image that Augusta and Columbia sit at the inland limits of broad flood plains of their rivers. The same is true but less pronounced for the other cities and their rivers.
These examples of Fall Line cities in the southeast are far from unique. Farther north, Richmond, VA, Washington, DC, Baltimore, MD, and Philadelphia, PA all sit on the Fall Line, as can be seen on an accompanying page.
Back to the GEOL 1122 main page.