[2] The island, a California Historical Landmark,[1] has been used by humans for a variety of purposes, including seasonal hunting and gathering by Indigenous peoples, water and timber supply for European ships, ranching by Mexicans, United States military installations, a United States Public Health Service Quarantine Station, and a U.S. Bureau of Immigration inspection and detention facility.

[6] Angel Island emerged during the last Ice Age when the ocean, much lower and located miles to the west, shaped the landscape.

[9] The island's form is roughly, featuring steep ridges radiating from the central peak of the Mount Caroline Livermore.

[10] The Franciscan Complex rocks are unconformably overlain by flat-lying sediments of the Colma Formation near Blunt Point on the south coast of the island.

[10] These sandstones are only weakly consolidated and are eroding to provide a supply of sand to the south coast of the island, in contrast to the northern and western beaches which are dominated by pebbles and cobbles.

[11] Until about 10,000 years ago, Angel Island was connected to the mainland; it was cut off by the rise in sea levels due to the end of the last ice age.

Similar evidence of Native American settlement is found on the nearby mainland of the Tiburon Peninsula upon Ring Mountain.

In 1867, General McDowell took control of the quarry and used it for Army construction at Fort Point, the San Francisco Presidio, and on Angel Island itself.

It continued to serve as a transit station throughout the first half of the 20th century, with troops engaged in World War I embarking and returning there.

[21] In 1938, hearings concerning charges of membership in the Communist political party against labor leader Harry Bridges were held on Angel Island before Dean James Landis of Harvard Law School.

Prior to the war, the infrastructure had been expanded, including building the Army ferry USAT General Frank M. Coxe, which transported troops to and from Angel Island on a regular schedule.

Fort McDowell was used as a detention station for Japanese, German and Italian immigrant residents of Hawaii arrested as potential fifth columnists (despite a lack of supporting evidence or access to due process).

After World War II ended, the reorganization of the San Francisco Port of Embarkation did not include Fort McDowell, and the post was decommissioned on August 28, 1946.

[26] The bubonic plague posed such a threat to the U.S. that Angel Island opened as a quarantine station in 1891 to screen Asian passengers and their baggage prior to landing on U.S.

[28] The compound contained many separate buildings including detention barracks, disinfection facilities, convalescence quarters, and an isolation hospital that was known as the "leper's house".

[29] In response to the death of Wong Chut King, a Chinese immigrant who worked in a rat-infested lumberyard in Chinatown, the San Francisco Health Board quickly quarantined the local area to neutralize possible disease-causing agents.

[27] After more deaths, tissue samples were sent to Angel Island for testing to determine if they harbored Yersinia pestis, the bacteria responsible for spreading the bubonic plague.

Bacteriologist Joseph J. Kinyoun, who was stationed at Angel Island in 1899, believed that the plague would spread throughout San Francisco's Chinatown.

[35] A person's racial identity and social class determined the intensity of the examination imposed, resulting in fewer white Europeans and American citizens being subjected to the inspections.

After sitting vacant since World War II, the hospital near the detention barrack was renovated, at a cost of $15 million from a variety of federal, state and private sources, and opened as a museum in 2022.

The last federal Department of Defense personnel withdrew in 1962, turning over the entire island as a state park in December of the same year.

The island's native plant communities include coastal grassland and coastal scrub, mostly on the island's south- and west-facing slopes and ridge tops, and evergreen woodland – predominantly of Coast Live Oak (Quercus agrifolia), bay (Umbellularia californica), toyon (Heteromeles arbutifolia), and madrone (Arbutus menziesii), with California Hazelnut (Corylus cornuta) and Western Sword Fern (Polystichum munitum) in the understory – on the eastern and northern portions of the island sheltered from the westerly winds from the Golden Gate.

In the 1980s, California State Parks undertook environmental studies to remove most of the Eucalyptus from the island, in order to restore native flora and reduce fire danger.

[40] In addition to the eucalyptus, plantings from the military period of Monterey Pine (Pinus radiata), Cork Oak (Quercus suber), Australian Blackwood (Acacia melanoxylon), Canary Island Date Palm (Phoenix canariensis), Century Plant (Agave americana), Japanese Redwood (Cryptomeria japonica), Incense Cedar (Calocedrus decurrens), Deodar Cedar (Cedrus deodara), Coast Redwood (Sequoia sempervirens), Giant Sequoia (Sequoiadendron giganteum), Norfolk Island Pine (Araucaria heterophylla), Monkey puzzle tree (Araucaria araucana) and others can be found in and around the former military bases and immigration station.

[41] In 2002, the summit of Mount Caroline Livermore, which had been flattened in the 1950s to build the Nike missile radar and tracking installation, was re-contoured to resemble its original appearance, and increased 16 feet in height as a result.

[42] On October 12, 2008, at approximately 9 p.m. PDT, a fire visible from all around the San Francisco Bay broke out on the island and spread to an estimated 100 acres (40 ha) within an hour.

[46] The fire burned several stands of Monterey Pine (Pinus radiata) originally planted by the U.S. Army, which will be restored to native evergreen woodlands.

[49][page needed] Instead of replacing the cables, PG&E is investigating using the island for a distributed energy resources microgrid pilot project.