{"nrhp_refnum":"100011433","name":"Marconi Wireless-Synanon Tomales Bay Headquarters Historic District (Boundary Increase)","other_names":["Marconi Property"],"category":"district","location":{"address":"18500 CA 1","address_restricted":false,"city":"Marshall","county":"Marin County","state":"CA","lat":null,"lon":null,"geom_source":null},"listed_date":"2025-01-31","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Communications"],"significance_levels":["national"],"summary":{"what_it_is":"A seven-acre district on the east shore of Tomales Bay in Marshall, Marin County, California, containing 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 station was the receiving half, paired with a transmitter at Bolinas, of the first dependable wireless link between the continental United States and Hawaii, and through Hawaii to Japan. It also provided ship-to-shore service across the Pacific. The form argues national significance for its role in starting trans-Pacific radio communication.","narrative":"Four buildings on the east shore of Tomales Bay in Marshall, California, survive from Station KPH, a wireless receiving station built in 1913 by the J.G. White Engineering Company for the Marconi Wireless Telegraph Company of America. They are a two-story hotel for operators and guests, a powerhouse, and two cottages for the station's managers. All are steel-frame and concrete buildings with red tile roofs. The hotel has a long veranda on 35 concrete pillars and stone fireplaces in the lobby and billiard room. Dedicated in 1914, the station worked with a transmitter at Bolinas to open dependable communication between California and Hawaii, and onward to Japan, and it also served ships across the Pacific. The Navy took it over in 1917, and the Radio Corporation of America operated it from 1920 until radio work moved to Point Reyes in 1931. The nominated parcel excludes the original operating building and later buildings constructed during Synanon's 1965 to 1980 occupancy.","period_of_significance":"1914-1931","architect_builder":"J.G. White Engineering Company of New York City (listed on the form as J.C. White, Engineering Company)","architectural_style":"Late 19th and 20th Century Revivals","criteria":["A"],"status_note":"Rehabilitation for use as a non-profit conference center was under way when the form was prepared; the roofs were described as in good condition and the exteriors largely unchanged.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:54:29.414316-05","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-boundary-inc-100011433/"}