Editing Potomac River (section)

===Natural history===
The river itself is at least 3.5 million years old,<ref name="NPS-PH" /> likely extending back ten to twenty million years before the present when the Atlantic Ocean lowered and exposed coastal sediments along the fall line. This included the area at Great Falls, which eroded into its present form during recent glaciation periods.<ref name=USGS>{{cite web |title=The River and the Rocks: The Geologic Story of Great Falls and the Potomac River Gorge |last=Reed |first=John Calvin |url=https://pubs.usgs.gov/bul/1471/report.pdf |website=pubs.usgs.gov |publisher=USGS |access-date=24 March 2019 |archive-date=October 1, 2020 |archive-url=https://web.archive.org/web/20201001233035/https://pubs.usgs.gov/bul/1471/report.pdf |url-status=live}}</ref>

The [[stream gradient]] of the entire river is 0.14%, a drop of 930 m over 652&nbsp;km.