{"nrhp_refnum":"04000014","name":"Mountain Quarries Bridge","other_names":["Mountain Quarry Cement Bridge","American River Quarry Bridge","Pacific Portland Cement Company Railroad Bridge"],"category":"structure","location":{"address":"North Fork of the American River","address_restricted":false,"city":"Auburn","county":"Placer County","state":"CA","lat":38.912575494000066,"lon":-121.041455483,"geom_source":"nps_gis"},"listed_date":"2004-02-11","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering"],"significance_levels":["state"],"summary":{"what_it_is":"A single-track reinforced concrete railroad arch bridge across the American River just below the confluence of its North and Middle Forks, about a mile east of Auburn on the Placer and El Dorado County line, California. It was built 1910-1912 for the Mountain Quarries Company.","why_significant":"The nomination argues the bridge meets Criterion C for distinctive engineering, as an early and rare use of reinforced concrete in a railroad bridge and the work of engineer John B. Leonard. It was designed to carry heavy Mallet locomotives across a restricted, skewed canyon site. It has survived major floods that destroyed newer bridges upstream.","narrative":"Spanning the American River just below the meeting of its North and Middle Forks near Auburn, this reinforced concrete railroad bridge was built between 1910 and 1912 for the Mountain Quarries Company, a subsidiary of Pacific Portland Cement Company. It carries a single track on three 140-foot skewed arches, stands 70 feet high, and measures about 650 feet including its approaches. Engineer John B. Leonard designed it to bear heavy Mallet locomotives hauling limestone from the quarry to the rail line at Auburn. Its skewed piers answer the narrow, steep canyon, and it cost about twenty percent less than a comparable steel structure. The bridge was listed for its engineering under Criterion C, as an early and rare use of reinforced concrete in railroading. It withstood floods that destroyed newer highway bridges upstream and served as a vehicle detour in 1964-65. Rail use ended around 1940, and today hikers and riders cross it on a recreation trail.","period_of_significance":"1912","architect_builder":"Mr. John B. Leonard, of the firm Leonard & Day, Engineer; Duncanson-Harrelson Company, Building Contractors; J.B. Harrington, Chief Construction Engineer","architectural_style":"Other - Concrete Arch Bridge","criteria":["C"],"status_note":"Rail service ended around 1939-1940 and the tracks were removed; the bridge is now used by pedestrians and equestrians. A pier foundation was stabilized and repaired in the late 1990s.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:54:29.707568-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/04000014.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/04000014/c55564710b-800.webp","url_1600":"https://nationalhistoricalregister.com/media/04000014/c55564710b-1600.webp","licence":"CC BY-SA 3.0","author":"liannadavis","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Mountain_Quarries_Bridge_2012-09-16_16-32-00.jpg\" rel=\"noopener\">liannadavis</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:Mountain_Quarries_Bridge_2012-09-16_16-32-00.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123860404","wikipedia":"https://en.wikipedia.org/wiki/Mountain_Quarries_Bridge","wikidata":"https://www.wikidata.org/wiki/Q14683436"},"indexable":true,"url":"https://nationalhistoricalregister.com/california/placer-county/mountain-quarries-bridge-04000014/"}