{"nrhp_refnum":"75000438","name":"Big Gap Flume","other_names":[],"category":"site","location":{"address":"E of Groveland off CA 120 in Stanislaus National Forest","address_restricted":false,"city":"Groveland","county":"Mariposa County","state":"CA","lat":37.82196977900003,"lon":-120.06058123599996,"geom_source":"nps_gis"},"listed_date":"1975-05-12","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Industry","Engineering","Social History"],"significance_levels":["local"],"summary":{"what_it_is":"A historic site on the Stanislaus National Forest off Highway 120 near Buck Meadows and Groveland, Mariposa County, California. It holds remains of a suspended wooden flume built in 1859 and a later iron siphon pipe that carried water across Conrad Gulch.","why_significant":"The flume was the key engineering link in the Golden Rock Water Ditch, a gravity-flow system that supplied water to gold miners in Mariposa and Tuolumne Counties. The 2,200-foot wooden flume, with eleven towers up to 265 feet high, was considered a remarkable feat for 1859. The replacement pipe, built in 1869 with the labor of about 2,000 miners, still crosses the gulch.","narrative":"Big Gap Flume is a site in the Stanislaus National Forest, east of Groveland off State Highway 120, where a water ditch once crossed Conrad Gulch. Built in 1859 to a design by G. W. Holt, the suspended wooden flume ran 2,200 feet on eleven towers, the tallest 265 feet, and carried water for gold mining in Mariposa and Tuolumne Counties. It was part of the 36-mile Golden Rock Water Ditch, much of which Chinese laborers dug with picks and shovels. The flume fell in 1868. Andrew Rocca replaced it with a riveted iron siphon pipe 2,262 feet long, finished in July 1869 with help from about 2,000 miners. The ditch later served mining companies, electrical power and fire protection, and was sold for delinquent taxes in 1942. Today the cable anchor mounds, trench-like footing lines and the hand-riveted pipe, without its trestle, mark the site.","period_of_significance":"1859-1942","architect_builder":"Engineer G. W. Holt (design); builders G. W. Holt and Conrad; Golden Rock Water Company","architectural_style":null,"criteria":[],"status_note":"Condition deteriorated and altered; only a few remains of the wooden flume survive, and the later pipe remains without its trestle work. Function listed as abandoned, not in use.","vacant_flag":true,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:31.58285-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/75000438.pdf"},"photo":null,"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123859730","wikipedia":null,"wikidata":null},"indexable":true,"url":"https://nationalhistoricalregister.com/california/mariposa-county/big-gap-flume-75000438/"}