Editing Potomac River (section)

===Notes===
*{{cnote|AQU|The diversion dam at Great Falls, often called the [[Washington Aqueduct|"Aqueduct Dam"]], was built in the 1850s by the US Army Corps of Engineers as part of the project assigned to them by Congress to supply clean water from above Great Falls to Washington, DC. Water diverted by the dam flows 12 miles through a 9-foot diameter pipeline to Dalecarlia Reservoir on the outskirts of the city where it is first allowed to settle and then filtered and purified before being distributed to consumers. Since 1927, potable water from Dalecarlia has also been provided to Arlington County and some other sections of nearby northern Virginia through three 20-inch diameter pipelines that cross the Potomac under the deck of Chain Bridge. In addition, there is nearby a 4-foot diameter conduit constructed in 1967 that traverses the Potomac beneath the riverbed which is used primarily for backup purposes.<ref>[https://archive.today/20180219231327/https://www.washingtonian.com/2007/03/01/water-water/ "Water, Water ... "] by Larry Van Dyne, ''Washingtonian Magazine'' (March 2007)</ref><ref>[https://archive.today/20180219231922/http://www.virginiaplaces.org/nova/watersourcesnova.html "Sources of Northern Virginia Drinking Water"], ''Virginia Places''</ref> }}
*{{cnote|GHL|"Evidence of the ancient Potomac River bed can be seen in well-rounded boulders, smoothed surfaces and grooves, and beautifully formed potholes. Look for sandstone boulders along the trail, which were deposited by massive floods. The sandy soils along the river trail, with shells mixed in, are a result of sediment deposits from floods. Some of the oldest sediment deposits in the area can be found on '''Glade Hill''', between the Matildaville and Carriage Road trails. '''Glade Hill''' was once an island in the Potomac River, and the deposits found there were left before Mather Gorge formed."<ref>[https://www.nps.gov/grfa/learn/nature/geology.htm Great Falls Geology] {{Webarchive|url=https://web.archive.org/web/20180104015155/https://www.nps.gov/grfa/learn/nature/geology.htm |date=January 4, 2018 }}, National Park Service, April 10, 2015</ref> }}
*{{cnote|PIF|"In the Late Pennsylvanian, the rocks of the Stubblefield Falls domain of the Mather Gorge Formation moved up relative to the Sykesville Formation on the steep, west-dipping Plummers Island fault and mylonite zones (Schoenborn, 2001) within an existing Plummers Island shear zone (figs. 5, 6). Shearing formed S2 cleavage with below-closure muscovite growth and more pervasive S2 cleavage in the Sykesville Formation. By the earliest Permian, all of the rocks in the Potomac terrane had cooled through 235°C (figs. 3, 5). Apatite fission-track data indicate cooling through ≈90°C to 100°C in Early Jurassic to Early Cretaceous time, with increasing ages to the east, suggesting kilometer-scale rotation of the Potomac terrane in the Cretaceous and (or) Tertiary, with the west side up."<ref>Michael J. Kunk, et al., [https://pubs.usgs.gov/circ/2004/1264/html/trip5/ Multiple Paleozoic Metamorphic Histories, Fabrics, and Faulting in the Westminster and Potomac Terranes, Central Appalachian Piedmont, Northern Virginia and Southern Maryland] {{Webarchive|url=https://web.archive.org/web/20171231212310/https://pubs.usgs.gov/circ/2004/1264/html/trip5/ |date=December 31, 2017 }}, U.S. Geological Survey, 23 November 2016</ref> }}
*{{cnote|BLK|"Two samples collected from the terrace dissected by Great Falls indicate that the Falls were established in their current location by 30 ky. A series of 6 samples taken from a vertical transect just below the falls, indicates that vertical incision continued a rate of 0.5 m/ky between 27 and 12 ky, increasing to nearly 1.0 m/ky during the Holocene. These data suggest that the drop over Great Falls is growing with time. A dramatic increase in outcrop weathering and soil depth 3.5 km downstream of the Falls, suggests that prior to establishment of the Great Falls knickzone, a similar feature was likely present near Black Pond. 10-Be data are not yet available for this paleo knick zone; however, a 10-Be model age >200 ky from the top of Plummers island 5 km down stream of Black Pond suggests a much older period of retreat led to the formation of the Black Pond paleo knick zone."<ref>Paul Bierman, et al., [https://gsa.confex.com/gsa/2004NE/finalprogram/abstract_69763.htm Great Falls is 30,000 Years Old] {{Webarchive|url=https://web.archive.org/web/20080907202524/http://gsa.confex.com/gsa/2004NE/finalprogram/abstract_69763.htm |date=September 7, 2008 }}, Paper No. 35-5, Session No. 35, Geomorphic Process Rates on the Passive Margin, March 26, 2004. Geological Society of America ''Abstracts with Programs'', Vol. 36, No. 2, p. 94</ref>}}
*{{cnote|PES|"The Potomac Estuary: From the Chain Bridge in Washington, DC, to Point Lookout at the confluence with the Chesapeake Bay, the Potomac Estuary is a long and narrow estuary—approximately 189 km. With its many tributaries and bays, however, the Potomac Estuary has a shoreline of 1,800 km. The Estuary meanders in a south, southeasterly direction, except for a sharp bend about halfway downriver. The Estuary has three well-defined and distinct zones. The upper zone, from Chain Bridge to Indian Head, is the tidal freshwater reach, with salinities of less than 0.5 parts per thousand (ppt). The middle reach, between Indian Head and the Route 301 Bridge at Morgantown, is the transition zone. The salinity of this zone varies from 0.5 to 7.0 ppt and is often referred to as the zone of maximum turbidity. The lower zone, from the 301 Bridge to Point Lookout, has salinities ranging from 7 to 16 ppt."<ref>{{Cite web |url=http://www.potomacriver.org/wp-content/uploads/2015/07/NAJ_01_Chap1.pdf |title=Chapter One: Introduction |access-date=December 30, 2017 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207143813/http://www.potomacriver.org/wp-content/uploads/2015/07/NAJ_01_Chap1.pdf |url-status=live}}</ref> }}
*{{cnote|TRI|The rocky western (upriver) and central portions of the island are part of the Piedmont Plateau, while the southeastern part is within the Atlantic Coastal Plain. At one point opposite Georgetown, the Atlantic Seaboard fall line between the Piedmont and the Coastal Plain can be seen as a natural phenomenon. The island has about {{convert|2.5|mi|km|adj=on}} of shoreline, and the highest area of the island (where the Mason mansion stood) is about {{convert|44|ft|m}} above sea level.<!-- Text copied from [[Theodore Roosevelt Island#Geography and natural history]] April 2018 -->}}