{"nrhp_refnum":"88003223","name":"Marconi Wireless-Synanon Tomales Bay Headquarters Historic District (Additional Documentation)","other_names":["Marconi Property","Station KPH- Marconi Wireless Telegraph Company of America Historic District (Old Name)","Synanon “Bay Ranch”"],"category":"district","location":{"address":"18500 CA 1","address_restricted":false,"city":"Marshall","county":"Marin County","state":"CA","lat":38.14407097700007,"lon":-122.87842704299999,"geom_source":"nps_gis"},"listed_date":"1989-07-24","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Communications","Architecture","Social History"],"significance_levels":["local"],"summary":{"what_it_is":"A seven-acre historic district at 18500 State Highway 1 in Marshall, Marin County, California, on the east shore of Tomales Bay. It holds four of the five buildings built in 1913 for Marconi's Station KPH wireless receiving station: a hotel, a powerhouse and two cottages.","why_significant":"The nomination argues the station was the receiving half, with the Bolinas transmitter, of the first dependable wireless link between the continental United States and Hawaii, and through Hawaii to Japan. It also provided ship-to-shore communication across the Pacific. It is nominated at the national level for its role in starting trans-Pacific radio communication.","narrative":"Four concrete and steel-frame buildings on Tomales Bay in Marshall, California, remain from Station KPH, a wireless receiving station built in 1913 for the Marconi Wireless Telegraph Company of America. The district includes a two-story hotel with a long tile-roofed veranda, a powerhouse, and two cottages that housed the station's managers. Paired with a transmitting station at Bolinas, KPH opened in 1914 and gave the continental United States its first dependable wireless link to Hawaii, and through Hawaii to Japan. It also handled ship-to-shore traffic over the Pacific. The Navy took over the station in 1917, and the Radio Corporation of America ran it from 1920 until radio operations moved to Point Reyes in 1931. Synanon later used the property as its headquarters from 1965 to 1980. The nominated seven acres exclude the original operating building and later construction. The listing rests on the station's role in early trans-Pacific radio communication.","period_of_significance":"1914-1931","architect_builder":"White, J.C., Engineering Company (the significance text names it the J.G. White Engineering Company of New York City)","architectural_style":"Late 19th and 20th Century Revivals","criteria":["A"],"status_note":"Work in progress: the owner, the California State Parks Foundation, planned to rehabilitate the buildings as a non-profit conference center. The tile roofs are reported in good condition.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:54:27.484543-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/88003223.pdf"},"photo":null,"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123859717","wikipedia":null,"wikidata":null},"indexable":true,"url":"https://nationalhistoricalregister.com/california/marin-county/marconi-wireless-synanon-tomales-bay-headquarters-historic-district-additional-d-88003223/"}