Fall line

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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.[1] A fall line often will recede upstream as the river cuts out the uphill dense material, forming "c"-shaped waterfalls and exposing bedrock shoals. Because of these features, riverboats typically cannot travel any farther inland without portaging, unless locks are built. The rapid change in elevation of the water and resulting energy release make the fall line a good location for water mills, grist mills, and sawmills. Seeking a head of navigation with a ready supply of water power, people have long made settlements where rivers cross a fall line.


Diagram showing the Fall Line. USGS figure.

The slope of fall zones on rivers played a role in settlement patterns. For example, the fall line represents the inland limit of navigation on many rivers. As such, many fall line cities grew around transferring people and goods between land-based and water-based transportation at this point.[2]

Atlantic Seaboard Fall Line[edit]

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The Atlantic Seaboard Fall Line, or Fall Zone, is a 1,400-kilometre (900-mile) escarpment where the Piedmont and Atlantic Coastal Plain meet in the eastern United States.[3] Much of the Atlantic Seaboard fall line passes through areas where no evidence of faulting is present.

The fall line marks the geologic boundary of hard metamorphosed terrain—the product of the Taconic orogeny—and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated Cretaceous and Tertiary sediments. Examples of the Fall Zone include the Potomac River's Little Falls and the rapids in Richmond, Virginia, where the James River falls across a series of rapids down to the tidal estuary of the James River. Columbia, South Carolina is similar as well with the Congaree River.

Before navigation improvements such as locks, the fall line was often the head of navigation on rivers due to rapids and waterfalls, such as the Little Falls of the Potomac River. Numerous cities were founded at the intersection of rivers and the fall line. U.S. Route 1 links many of the fall line cities.

Mid-Atlantic and Southern U.S. fall line cities include:


The Laurentian Upland forms a long scarp line where it meets the Great Lakes–St. Lawrence Lowlands. Along this line numerous rivers have carved falls and canyons (listed East to West):

The Jacques-Cartier River and Saint-Maurice River lack such noticeable feature because they cross the scarp through U-shaped valleys. The falls of the lower Saint-Maurice (as well as those of the Beauport River, in Quebec City) are due to the fluvial terraces of the Saint Lawrence river rather than the Laurentian Scarp.

See also[edit]


  1. ^ Schneider, Craig W.; Richard B. Searles (1991). Seaweeds of the southeastern United States: Cape Hatteras to Cape Canaveral. Duke University Press. pp. 5–7. ISBN 978-0-8223-1101-0. Retrieved 17 November 2010.
  2. ^ a b "The Fall Line and major cities of the Eastern U.S."
  3. ^ a b c Freitag, Bob; Susan Bolton; Frank Westerlund; Julie Clark (2009). Floodplain Management: A New Approach for a New Era. Island Press. p. 77. ISBN 978-1-59726-635-2. Retrieved 17 November 2010.
  4. ^ Shamsi, Nayyar (2006). Encyclopaedia of Political Geography. Anmol Publications. pp. 92–93. ISBN 978-81-261-2406-0. Retrieved 17 November 2010.
  5. ^ a b c d e f g Dunkerly, Robert; Boland, Irene (2017). Eutaw Springs. Columbia: The University of South Carolina Press. p. 24. ISBN 9781611177589.
  6. ^ "A Summary of the Geologic History of Delaware". The Delaware Geological Survey. Retrieved 25 January 2017.
  7. ^ "Maryland Geology". Maryland Geological Society. Retrieved 25 January 2017.
  8. ^ a b c d "Geology of the Fall Line". Virginia Places. Retrieved 25 January 2017.
  9. ^ a b c "Fall Line". NCpedia. Retrieved 25 January 2017.
  10. ^ a b c "Fall Line". The New Georgia Encyclopedia. Retrieved 17 October 2011.
  11. ^ a b c "Fall Line". Encyclopedia of Alabama. Retrieved 25 January 2017.

External links[edit]