{"nrhp_refnum":"66000225","name":"Old Mission Dam","other_names":["Padre Dam"],"category":"structure","location":{"address":"N side of Mission St.-Gorge Rd.","address_restricted":false,"city":"San Diego","county":"San Diego County","state":"CA","lat":32.83970749650007,"lon":-117.04321585593904,"geom_source":"nps_gis"},"listed_date":"1966-10-15","is_nhl":true,"nhl_designated_date":"1963-05-21","areas_of_significance":["Engineering","Agriculture"],"significance_levels":["national"],"summary":{"what_it_is":"A historic cobblestone-and-cement irrigation dam on the San Diego River at the head of Mission Gorge, north of Mission Street on Gorge Road in San Diego, California. It was built for the Mission San Diego de Alcala, probably beginning around 1803.","why_significant":"The dam, with its aqueduct and flume running about five miles to the mission, is described as perhaps the first major irrigation-engineering project on the Pacific Coast of the United States. It gave the mission a year-round water supply for fields, milling and domestic use. Only the dam survives in meaningful form, and it still backs up some water.","narrative":"Old Mission Dam is a cobblestone-and-cement structure across the San Diego River near the head of Mission Gorge in San Diego. Originally about 220 feet long, 12 feet high and 13 feet thick, it was built to hold back river water that ran dry in summer. A gate released water as needed, and a tile flume resting on cobblestones and cement carried it roughly five miles to Mission San Diego de Alcala. The dam was probably begun around 1803, after drought years, and the irrigation system had reached its final form by 1817. It supplied the mission's fields, mill and household needs through the year, and is regarded as perhaps the first major irrigation-engineering project on the Pacific Coast of the United States. Floods and neglect left the works in ruins by 1867, though the dam was repaired about 1874. A large part of it still stands and holds back water, but almost nothing of the aqueduct remains. The listed area is about a quarter acre around the dam.","period_of_significance":"1800-1899","architect_builder":null,"architectural_style":null,"criteria":[],"status_note":"Condition marked deteriorated and unaltered; a considerable portion of the dam still stands and impounds water, while nearly all of the aqueduct is gone. The dam is publicly owned and used as a park and historic site.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:32.243029-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/66000225_NHL.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/66000225/290a9edde5-800.webp","url_1600":"https://nationalhistoricalregister.com/media/66000225/290a9edde5-1600.webp","licence":"CC BY-SA 3.0","author":"Dmadeo","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Old-mission-dam.JPG\" rel=\"noopener\">Dmadeo</a>, <a href=\"https://creativecommons.org/licenses/by-sa/3.0\" rel=\"license noopener\">CC BY-SA 3.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Old-mission-dam.JPG"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123858032","wikipedia":"https://en.wikipedia.org/wiki/Old_Mission_Dam","wikidata":"https://www.wikidata.org/wiki/Q7084554"},"indexable":true,"url":"https://nationalhistoricalregister.com/california/san-diego-county/old-mission-dam-66000225/"}