{"nrhp_refnum":"79003038","name":"Potomac Canal Historic District","other_names":["Patowmack Canal Historic District"],"category":"district","location":{"address":"E of Great Falls","address_restricted":false,"city":"Great Falls","county":"Fairfax (city and county)","state":"VA","lat":38.996656584500045,"lon":-77.25274654187865,"geom_source":"nps_gis"},"listed_date":"1979-10-18","is_nhl":true,"nhl_designated_date":"1982-12-17","areas_of_significance":["Engineering","Politics/Government"],"significance_levels":["national"],"summary":{"what_it_is":"A ruined skirting canal about three-quarters of a mile long within Great Falls Park, Fairfax County, Virginia, built between 1785 and 1802 by the Patowmack Canal Company to bypass the Great Falls of the Potomac. It includes five locks, a holding basin, guard gates, a wing dam and associated ruins.","why_significant":"The canal was the largest of five skirting canals on the Potomac and an early, significant American engineering achievement, since canals with locks were uncommon at the time. Its lower locks were blasted from bedrock with black powder, one of the first uses of explosives in American engineering. It was one of the first state-financed internal improvements, promoted by George Washington, and it also includes the ruins of the speculative town of Matildaville.","narrative":"Within Great Falls Park in Fairfax County, Virginia, lie the remains of a canal built to carry boats around the Great Falls of the Potomac. The Patowmack Canal Company worked on it from 1785 to 1802. The route runs about three-quarters of a mile and once had a wing dam, guard gates, a two-acre holding basin and five locks. The lowest locks were blasted from solid rock with black powder in hand-drilled holes. The canal was part of a plan, backed by George Washington, to make the Potomac navigable toward the Ohio country, and Maryland and Virginia bought nearly half the company's shares. The company failed financially and dissolved in 1826. Nearby ruins include the planned town of Matildaville, founded by Henry Lee, along with mill and foundry sites, a log inn and a superintendent's house. Today the canal is a ruin, but it preserves significant evidence of early American canal engineering and state-backed commercial ambition.","period_of_significance":"1785-1830","architect_builder":"Patowmack Canal Company; John Rumsey appears to have been the principal engineer","architectural_style":null,"criteria":[],"status_note":"Described as in ruins: much of the canal bed is filled with debris and silt, the lock gates were dismantled in 1830, and the associated structures survive only as foundations or ruins.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:51:56.757296-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/33/6805/41680533/content/electronic-records/rg-079/NPS_VA/79003038.pdf"},"photo":null,"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/41680533","wikipedia":"https://en.wikipedia.org/wiki/Potomac_Canal_Historic_District","wikidata":"https://www.wikidata.org/wiki/Q7235044"},"indexable":true,"url":"https://nationalhistoricalregister.com/virginia/fairfax/potomac-canal-historic-district-79003038/"}