Angel Island

Angel Island is the largest natural island in San Francisco Bay, about 740 acres / 3 km² of steep, rounded hills that climb to Mount Caroline Livermore, 788 feet / 240 m above the water. Only Alameda is bigger, and Alameda became an island only when a tidal canal was cut in 1902. Angel Island lies in the bay's northern half, separated from the Tiburon Peninsula of Marin County by Raccoon Strait, a channel about 90 feet / 27 m deep, and it is reachable only by boat.

Almost all of the island belongs to Marin County, inside the town of Tiburon. A thin slice of its eastern end, around Fort McDowell and Point Blunt, falls within the City and County of San Francisco. The bedrock belongs to the Franciscan Complex, a jumble of ocean-floor sediment and volcanic rock scraped onto the continent and squeezed in an ancient subduction zone. Minerals such as jadeite and glaucophane, which form only under high pressure, record that deep burial. From the summit, the view takes in the San Francisco skyline, the Marin Headlands and Mount Tamalpais.

In 1775 the Spanish commander Juan Manuel de Ayala anchored the San Carlos in the sheltered cove on the island's north side, now Ayala Cove, and named the island Isla de los Ángeles. Its position near the bay entrance later made it useful to the Army, which kept posts there until 1962, and to the federal government, which ran an immigration station there from 1910 to 1940. That station processed hundreds of thousands of arrivals, most of them from China, until a fire destroyed its administration building.

The park began in 1955 with 38 acres around Ayala Cove. After the military left in 1962, the whole island became Angel Island State Park that December. Ferries run from Tiburon and from San Francisco, landing at Ayala Cove, with reduced service from October through March, and trails and a perimeter road circle the island and climb to the summit.