"Potowmack River then, is the centre of the Union."
This map of the Potomac River dates to 1813. It is entitled “Plan of that part of Potowmack River which applies to the first report on defencible positions by William Tatham.” Great Falls appears at the far right of the map, with Alexandria also visible at the far right; the map then shows the path of the river all the way south to the Chesapeake Bay. This map and its notations concerning tides and winds illustrate both the early importance of the river to the development of this area and some of the challenges it has always posed to navigation.
The earliest European explorers believed the Potomac might be the key to the Northwest Passage and a route to China, while George Washington was later convinced that it was an ideal route to westward expansion. Alexandrians invested heavily in the Potomac Company (second as a group only to the government) and its efforts to clear the river and build canals around Little Falls and Great Falls (Littlefield, p. 10).
The Potomac River is a tidal estuary; it contains numerous islands, sandbars, and shoals, and is prone to silting. Therefore, it requires occasional dredging and is difficult to navigate. In addition to tidal currents which are affected by wind direction, the river also has half-tides (occasional currents running opposite the main current in the channel). The depth of the channel has varied over time due to silting, so accurate charts, buoys and lighthouses, and knowledgeable pilots have been and remain essential to successful navigation of the Potomac.
The Jones Point Lighthouse site was purchased in 1855; a combination lighthouse and dwelling was built, and the first lighting was May 3, 1856. At first the light was fixed white, before it became fixed red in 1900 and flashing white (every six seconds) in 1919. In 1926, an iron tower with a fixed green light was built, although a keeper remained in the original building until 1934. For most of the period of operation of the lighthouse (from 1866-1934), the keepers were members of or relatives of the Greenwood family. The lighthouse was deactivated in 1962, and boaters now use the lights of the Wilson Bridge for orientation. The site is now owned by the National Park Service. Jones Point and the southern District of Columbia cornerstone are listed in the National Register of Historic Places and have been documented by the Historic American Buildings Survey.