{"nrhp_refnum":"77000318","name":"Empire Mine","other_names":["Empire Mine State Historic Park"],"category":"district","location":{"address":"SE of Grass Valley at 338 E. Empire St.","address_restricted":false,"city":"Grass Valley","county":"Nevada County","state":"CA","lat":39.20351929850003,"lon":-121.0490569005712,"geom_source":"nps_gis"},"listed_date":"1977-12-09","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Industry","Architecture"],"significance_levels":["state"],"summary":{"what_it_is":"A historic gold mining district in Grass Valley, Nevada County, California, now a state historic park. It includes the Empire Cottage (Bourn mansion, built 1896), the mine office and refinery (circa 1899), and the Empire clubhouse (circa 1905), all designed by architect Willis Polk.","why_significant":"The Empire Mine was the oldest quartz mine in continuous operation in the United States when it closed in 1956, and it yielded an estimated $120 million in gold. The nomination also stresses the architectural value of the Polk-designed buildings built for mine owner William B. Bourn II, with their restrained forms and local stone and brick construction.","narrative":"Empire Mine State Historic Park in Grass Valley preserves the surface buildings of one of the richest gold mines in the world. Mining began after George D. Roberts found a gold-bearing ledge on the hillside in 1850. The mine passed through several owners, and William B. Bourn took over management in 1867. It later merged with the neighboring Pennsylvania and North Star groups. When it closed in 1956, it was the oldest quartz mine in continuous operation in the United States, with an estimated $120 million in gold recovered. Surviving structures include the 1896 Bourn mansion, built of rough granite and brick, the mine office and refinery, and the circa 1905 clubhouse. San Francisco architect Willis Polk designed the mansion, office and clubhouse. Quarry stone from the mine was used in the walls. The mansion sits among tall pines, behind ornate brick and rock walls, and shows its age through weathered mortar and broken leaded windows.","period_of_significance":"1800-1899, 1900-","architect_builder":"Willis Polk (architect); William B. Bourn, Jr. (owner)","architectural_style":null,"criteria":[],"status_note":"The Bourn mansion has not been lived in for several years and shows deterioration, vandalism and moisture damage, though it is considered in fair condition. The clubhouse is leased to the Empire Club and described as in fair to good condition. The property is a public state park and museum.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:31.951572-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/77000318.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/77000318/cfe5faf1f2-800.webp","url_1600":"https://nationalhistoricalregister.com/media/77000318/cfe5faf1f2-1600.webp","licence":"CC BY 2.5","author":"Beej71","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Empire_mine_shaft.jpg\" rel=\"noopener\">Beej71</a>, <a href=\"https://creativecommons.org/licenses/by/2.5\" rel=\"license noopener\">CC BY 2.5</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Empire_mine_shaft.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123860129","wikipedia":"https://en.wikipedia.org/wiki/Empire_Mine_State_Historic_Park","wikidata":"https://www.wikidata.org/wiki/Q5374101"},"indexable":true,"url":"https://nationalhistoricalregister.com/california/nevada-county/empire-mine-77000318/"}