Atlantic Seaboard fall line

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Atlantic Seaboard fall line
Fall line
Nickname: Piedmont—Coastal Plain fall line
Country United States
North endpoint
South endpoint
New Jersey
Carolinas or Georgia
[1][2]
Length 900 mi (1,400 km) [2]
Map showing part of the Eastern Seaboard Fall Line where the pale colored coastal plain meets the brightly colored Piedmont.

The Atlantic Seaboard Fall Line, or Fall Zone, is a 900-mile (1,400 km) escarpment where the Piedmont and Atlantic coastal plain meet in the eastern United States.[2] 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 Cenozoic sediments. Examples of the Fall Zone include the Potomac River's Great Falls and the rapids in Richmond, Virginia, where the James River falls across a series of rapids down to its own tidal estuary.

Before navigation improvements such as locks, the fall line was generally the head of navigation on rivers due to their rapids or waterfalls, and the necessary portage around them. The Great Falls of the Potomac River is one example. Because of the commercial traffic, required labor and availability of water power to operate mills, numerous cities were founded at the intersection of rivers and the fall line. U.S. Route 1 links many of the fall line cities.

In 1808, Treasury Secretary Albert Gallatin noted the significance of the fall line as an obstacle to improved national communication and commerce between the Atlantic seaboard and the western river systems:[3]

The most prominent, though not perhaps the most insuperable obstacle in the navigation of the Atlantic rivers, consists in their lower falls, which are ascribed to a presumed continuous granite ridge, rising about one hundred and thirty feet above tide water. That ridge from New York to James River inclusively arrests the ascent of the tide; the falls of every river within that space being precisely at the head of the tide; pursuing thence southwardly a direction nearly parallel to the mountains, it recedes from the sea, leaving in each southern river an extent of good navigation between the tide and the falls. Other falls of less magnitude are found at the gaps of the Blue Ridge, through which the rivers have forced their passage...

Notable cities[edit]

Some cities that lie along the Piedmont—Coastal Plain fall line include the following (from north to south):


Atlantic Seaboard fall line, north-to-south
State Point (crossing) Elevation & coordinates Fall zone:
drop/width (slope)
Geomorphology
Piedmont—Coastal plain
New Jersey New Brunswick (Raritan River) 460 ft (140 m)40°29′18″N 74°26′52″W / 40.48833°N 74.44778°W / 40.48833; -74.44778
Trenton (Delaware River) 40°13′18″N 74°45′22″W / 40.22167°N 74.75611°W / 40.22167; -74.75611 8 ft
Pennsylvania Philadelphia (Schuylkill River by I-76)
Delaware Wilmington (Brandywine Creek)
Maryland Conowingo Dam (Susquehanna)
Ellicott City[7] (Patapsco) 39°16.044′N 76°47.573′W / 39.267400°N 76.792883°W / 39.267400; -76.792883[1] crystalline rock—unconsolidate marine sediments [2]
Great Falls (Potomac River) 38°59′51″N 77°15′9″W / 38.99750°N 77.25250°W / 38.99750; -77.25250 76 ft/<1 mi (>1.4%)
Virginia Fredericksburg (Rappahannock) 39°16.044′N 76°47.573′W / 39.267400°N 76.792883°W / 39.267400; -76.792883[3] [west of Interstate 95 bridge][8]
Emporia (Meherrin River)[9]

References[edit]

  1. ^ "The Fall Line". A Tapestry of Time and Terrain: The Union of Two Maps - Geology and Topography. USGS.gov. Retrieved 2010-08-12.  An alternate source claims the southern endpoint is farther west because there are "waterfalls & rapids":
    "Georgia Geology". Archived from the original on 4 September 2010. Retrieved 2010-08-13. 
  2. ^ a b c d e 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. 
  3. ^ [Report on] Roads and Canals, Communicated to the Senate April 4, 1808, p.729
  4. ^ a b 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 Deane, Winegar (2002). Highroad Guide to Chesapeake Bay. John F. Blair. p. 5. ISBN 978-0-89587-279-1. Retrieved 17 November 2010. 
  6. ^ a b Roberts, David C.; W. Grant Hodsdon (2001). Roger Tory Peterson, ed. A Field Guide to Geology: Eastern North America. Houghton Mifflin Harcourt. p. 242. ISBN 978-0-618-16438-7. Retrieved 17 November 2010. 
  7. ^ "History/Culture". PatapscoHeritageGreenway.org. Retrieved 2010-09-07. "George Ellicott House: A block away is the 1789 George Ellicott House at 24 Frederick Road., which has been saved, moved out of the flood plain, and restored. The Ellicott family settled here along the fall line of the Patapsco River in 1772 and built an innovative, water-powered flour mill" 
  8. ^ "Fall Line". VirginiaPlaces.org. Retrieved 2010-08-13. 
  9. ^ "River and "Fall Line" Cities". VirginiaPlaces.org. Retrieved 2010-08-13.