Tomales Bay is a long narrow inlet of the Pacific Ocean in Marin County in northern California in the United States. It is approximately 15 miles (25 km) long and averages nearly 1.0 miles (1.6 km) wide, effectively separating the Point Reyes Peninsula from the mainland of Marin County. It is located approximately 30 miles (48 km) northwest of San Francisco. The bay forms the eastern boundary of Point Reyes National Seashore. Tomales Bay is recognized for protection by the California Bays and Estuaries Policy. On its northern end it opens out onto Bodega Bay, which shelters it from the direct current of the Pacific. The bay is formed along a submerged portion of the San Andreas Fault.
Oyster farming is a major industry on the bay. The two largest producers are Tomales Bay Oyster Co and Hog Island Oyster Co, both of which retail oysters to the public and have picnic grounds on the east shore. Hillsides east of Tomales Bay are grazed by cows belonging to local dairies. There is also grazing land west of the bay, on farms and ranches leased from Point Reyes National Seashore.
The bay sees significant amounts of water sports including sailing, kayaking, and motorboating. Watercraft may be launched on Tomales Bay from the public boat ramp at Nick's Cove, north of Marshall. There is a $5 fee. The sand bar at the mouth of Tomales Bay is notoriously dangerous, with a long history of small boat accidents.
Towns bordering Tomales Bay include Inverness, Inverness Park, Point Reyes Station, and Marshall. Additional hamlets include Spengers, Duck Cove, Shallow Beach, and Vilicichs. Dillon Beach lies just to the north of the mouth of the bay, and Tomales just to the east.
The area was once Coast Miwok territory. Documented villages in the area included: Echa-kolum (south of Marshall), Sakloki (opposite Tomales Point), Shotommo-wi (near the mouth of the Estero de San Antonio), and Utumia (near Tomales).
The Giacomini Wetland Restoration Project, completed in 2008, returned to wetland several hundred acres at the south end of the bay that had been drained for grazing during the 1940s.
Marconi Conference Center 
The Marconi Conference Center State Historical Park|Marconi Conference Center SHP preserves a small hotel built by Guglielmo Marconi in 1913 to house personnel who staffed his transpacific radio receiver station nearby. The hotel and the associated operations building and employee cottages were built by the J.G. White Engineering Corp under contract to Marconi. RCA purchased the station from Marconi in 1920. The station was closed in 1939, though other nearby radio stations on the Point Reyes Peninsula still operate today. Synanon, a drug rehabilitation organization, owned it from the early 1960s until 1980, when it was purchased by a private foundation and given to the state in 1984 to operate as a conference center.
- State Water Resources Control Board Water Quality Control Policy for the Enclosed Bays and Estuaries of California (1974) State of California
- "Miwok Indian Tribe". Access Genealogy. Retrieved 2008-01-07.
- "Tomales Bay State Park". Retrieved 2008-01-07.
- David L. Durham (2000). Durhams' Place Names of the San Francisco Bay Area. Clovis, California: Word Dancer Press. ISBN 1-884995-35-7.
- Dickson, A. Bray Narrow Gauge to the Redwoods(1974)Trans-Anglo Books ISBN 87046-010-2
See also