Big Gap Flume
Why it's listed
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.
Significance in brief: 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.
Machine-generated summary. This summary was generated by a language model from the official nomination document and has not been reviewed line by line by an editor. It may contain errors. Check the source document before relying on any detail. Source: nomination document (PDF) · National Archives catalog entry. NRHP reference 75000438, listed May 12, 1975. Summary generated October 2026 (model claude-sonnet-5-5, prompt v1.0-2026-10-29, confidence medium).
Key facts
| Address | E of Groveland off CA 120 in Stanislaus National Forest, Groveland |
|---|---|
| County | Mariposa County |
| Listed | May 12, 1975 |
| Reference number | 75000438 |
| Resource type | Site |
| Period of significance | 1859-1942 |
| Architect / builder | Engineer G. W. Holt (design); builders G. W. Holt and Conrad; Golden Rock Water Company |
| Areas of significance | Industry, Engineering, Social History |
| Level of significance | Local |
| Status (as stated in the nomination) | 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. |
| Acreage | 0.3 |
| Coordinates | 37.82197, -120.06058 (NPS GIS) |
What listing means for this property
Sites (archaeological sites, battlefields, landscapes) are often listed with a restricted address to protect them from looting or disturbance. Listing is honorary for private owners; federal undertakings on or near the site go through Section 106 review, and state laws may protect burials and artefacts regardless of listing.
Noted as vacant in the nomination. Nomination documents can be decades old; current status may differ. If you are considering buying an empty listed property, read the due-diligence checklist.
General information, not legal or tax advice. Rules change; confirm with your State Historic Preservation Office or a qualified adviser.
Sources and further reading
- National Park Service, National Register of Historic Places database (snapshot May 2026), reference 75000438.
- Nomination form (PDF, National Archives) — catalog entry
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.