This list of islands of California is organized into sections, generally arranged from north to south. The islands within each section are listed in alphabetical order.
The Geographic Names Information System (GNIS) lists 527 named islands in the state.
Humboldt County
Offshore Island Image Coordinates DescriptionSugar Loaf IslandSugar Loaf Island, offshore Cape Mendocino, rises above mean sea level. It is a special zone in the South Cape Mendocino State Marine Reserve and is closed to public access.California Department of Fish and Wildlife, California Protected Marine Areas, 14 March 2013California Department of Fish and Wildlife, Sugarloaf Island Special Closure, 2015 Being offshore of Cape Mendocino, the westernmost point in California, Sugar Loaf Island is called the westernmost island in the state.
Humboldt Bay All three islands in Humboldt Bay are located in the narrow midsection of the bay. This portion of the bay is located within the City of Eureka, California entirely within Humboldt County. Island Image Coordinates Description Daby Island The smallest of the three islands within Humboldt Bay, Daby Island has a maximum elevation of and is located slightly northeast of Woodley Island.Tuluwat Island The largest island, long, was originally the center of culture and population of the indigenous Wiyot people. Now protected, no public access is allowed, except for the Wiyot and grandfathered residents. Woodley Island The second largest of the three islands within Humboldt Bay contains: the Woodley Island Marina (Eureka's largest marina), the Eureka regional office of the National Weather Service, and offices of the Humboldt Bay Harbor Recreation & Conservation District.
San Francisco Bay Area
Island Image Coordinates Counties DescriptionAlameda IslandAlameda, San Francisco (small, uninhabited sliver) This long island in San Francisco Bay is the main part of the City of Alameda.Alcatraz IslandSan FranciscoThis island in San Francisco Bay once served as a lighthouse, a military fortification, a military prison, and as a federal prison until 1963. It is now part of the Golden Gate National Recreation Area.Angel IslandMarin, San Francisco (small, uninhabited slivers) With an area of , this island in San Francisco Bay processed approximately 1 million immigrants to the U.S. during 1910 to 1940. It is currently a state park.Año Nuevo IslandSan MateoSmall Pacific island, about long, near Año Nuevo (New Year's) Point, south of the Golden Gate. It is protected by the Año Nuevo State Reserve as an important habitat for seabirds and other coastal wildlife.Bair IslandSan MateoThis island in San Francisco Bay near Redwood City is part of the Don Edwards San Francisco Bay National Wildlife Refuge.Bay Farm IslandAlamedaThis former island in San Francisco Bay has been connected to the mainland. It is part of the City of Alameda.Belvedere IslandMarinThis former island in Richardson Bay has been connected to the mainland. It is part of the City of Belvedere. Bird Island Marin Small Pacific island between Point Bonita and Rodeo Cove. Bird Rock Marin Small Pacific island west of Tomales Point, primarily a seabird colony. It covers . Brewer Island San Mateo Coterminous with Foster City. Brooks IslandContra Costa A island in San Francisco Bay south of Richmond, protected as part of the Brooks Island Regional Shoreline. The BrothersContra Costa Two small islands, East Brother and West Brother, located west of Point San Pablo. Each is about long. East Brother has a lighthouse and a bed and breakfast. Castro RocksContra CostaBeneath the Richmond–San Rafael Bridge. Coast Guard IslandAlameda Located in the Oakland Estuary, this artificial island is part of the City of Alameda. It is home to various United States Coast Guard facilities. Corinthian IslandMarin This former island was joined to the mainland in the 1980s. It is split between the city of Belvedere and the town of Tiburon. Dolphin Isle San Mateo Artificial island in Foster City Lagoon. Residential. Greco Island San Mateo This island in San Francisco Bay near Redwood City is part of the Don Edwards San Francisco Bay National Wildlife Refuge. Gull Rock Marin A Pacific island near Mount Tamalpais, about long. Hog Island (Petaluma River) Sonoma Island in the Petaluma River wetlands. Hog Island (Tomales Bay) Marin A island in Tomales Bay. Hooks Island Santa Clara tidal salt marsh island in the Palo Alto Baylands Nature Preserve Kent Island Marin An island in Bolinas Lagoon, near the town of Bolinas. About long. Mare Island Solano An island in San Pablo Bay near Vallejo. About long, site of a major shipyard. East Marin Island Marin Near San Rafael, California. Pictured on the right in the image. West Marin Island Marin Near San Rafael, California. Pictured on the left in the image. Mussel Rock San Mateo A stack in the Pacific Ocean near Daly City. About long. The Needles Marin Rock islets at Lime Point in Fort Baker near the Golden Gate Bridge's northern cable house. Newby Island Santa Clara Near Alviso, San Jose. Ogilvie Island Santa Clara Near Alviso, San Jose. Rat Rock Marin An tall rock north of China Camp. Red Rock IslandContra Costa, Marin and San Francisco This uninhabited island is located in San Francisco Bay just south of the Richmond–San Rafael Bridge, near the meeting point of three counties. It is privately owned. San Pedro Rock San Mateo A Pacific island near the city of Pacifica. About long. Seal Rocks (San Francisco, California) San Francisco A series of large rocks in the Pacific Ocean that host a sea lion colony. Seal Rock (San Mateo County, California)San Mateo A Pacific island south of Half Moon Bay, about long. The SistersMarin A pair of small islands in San Pablo Bay, south of Point Saint Pedro. Treasure IslandSan FranciscoThis artificial island in San Francisco Bay is tied to Yerba Buena Island. It was dredged out of the bay to house the Golden Gate International Exposition of 1939-40. Yerba Buena IslandSan FranciscoThis island in San Francisco Bay is home to a Coast Guard station. The San Francisco–Oakland Bay Bridge passes through it by means of a tunnel.
Farallon Islands The Farallon Islands are a group of rugged small islands over offshore from the mainland of the City and County of San Francisco, which they are also formally within. They consist of over twenty small islets divided into north, south and middle sections, as well as a major bank, Fanny Shoal. The surrounding waters were once used as a disposal site for radioactive waste.
Island Image Coordinates DescriptionAulone Island and Great Arch Rock North of Southeast Farallon Island, measuring wide and long.Drunk Uncle Islets Group of small islets north of Maintop Island.Farallón ViscaínoMiddle Farallon Island Medium-sized islet northwest of Southeast Farallon Island. It is long and has an area of .North Farallon Island Medium-sized islet long and high, covering .Peñasco QuebradoPiedra GuadalupeIsland of St. James Medium-sized islet in size, measuring long and high.Sea Lion Rock Small islet northwest of Aulon Island, about long.Seal Rock Small islet south of Southeast Farallon Island, with a maximum height of .Maintop Island West of Southeast Farallon Island, and has a maximum height of .Southeast Farallon Island Is the largest of the Farallons, covering . It is the only inhabited Farallon Island, and is also the site of Farallon Island Light.Sugarloaf Island Directly to the northeast of Aulone and Great Arch Rock, about high.
Suisun Bay Suisun Bay is an arm of the San Francisco Bay estuary which connects the Sacramento and San Joaquin Rivers to the Carquinez Strait.
Island Image Coordinates County Description Chipps Island Solano Dutton Island Solano Freeman Island Solano Small island, second from top on left hand of frame. Grizzly Island Solano Hammond Island Solano Joice Island Solano A marshy island long, north of Grizzly Bay. Morrow Island Solano A small island that has an elevation of 2 meters- 7 feet. Point Buckler Island Solano A private marshy island of , with some history as a kiteboarding destination. Roe Island Solano In Suisun Bay. On far right of picture (partially out of frame). Ryer Island Solano island, between Suisun Bay and Suisun Cutoff.David L. Durham, "California's Geographic Names: A Gazetteer of Historic and Modern Names of This State," p. 693 (Quill Driver Books 1998) . About long. Largest island in the photo. Seal Islands Contra Costa In Suisun Bay. Simmons Island Solano Snag Island Solano Smallest island in the photo, top center. Van Sickle Island Solano An island long at the junction of the Sacramento River, San Joaquin River, and Suisun Bay. Wheeler Island Solano
Sacramento–San Joaquin River Delta
The Sacramento–San Joaquin River Delta is an inverted delta at the juncture of the Sacramento and San Joaquin rivers. There are about 57 named islands in the Delta.