Marconi Wireless-Synanon Tomales Bay Headquarters Historic District (Additional Documentation)
Also known as: Marconi Property; Station KPH- Marconi Wireless Telegraph Company of America Historic District (Old Name); Synanon Bay Ranch
Why it's listed
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.
Significance in brief: 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.
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 88003223, listed July 24, 1989. Summary generated October 2026 (model claude-sonnet-5-5, prompt v1.0-2026-10-29, confidence medium).
Key facts
| Address | 18500 CA 1, Marshall |
|---|---|
| County | Marin County |
| Listed | July 24, 1989 |
| Reference number | 88003223 |
| Resource type | District |
| 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 |
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| Areas of significance | Communications, Architecture, Social History |
| Level of significance | Local |
| Status (as stated in the nomination) | 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. |
| Acreage | 62.29 |
| Coordinates | 38.14407, -122.87843 (NPS GIS) |
What listing means for this property
This is a historic district. Buildings within its boundary are either contributing (they add to the district's significance) or non-contributing. Owners of contributing income-producing buildings can claim the 20% federal rehabilitation tax credit; homeowners should look at state credits. National Register districts impose no design review by themselves; a local historic district ordinance, if one exists, does (the difference explained).
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 88003223.
- 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.