The first people to visit Alcatraz Island were indigenous peoples who arrived there between 10,000 and 20,000 years ago. Two large groups lived around the bay: the Miwok who lived north of the Bay in the current county of Marin, and the Ohlone who lived in coastal areas between Point Sur and the San Francisco Bay.
The early use of Alcatraz by these indigenous peoples is difficult to reconstruct because most oral histories of the tribes were lost. Historians believe that Alcatraz was used as a place for camping and an area for collecting food, especially eggs of birds and marine life. One tradition may have been that the Island was used as a place of exile for members of the tribe who had violated tribal law.

When the first Spanish explorers arrived in 1769, more than 10,000 indigenous people were living around San Francisco Bay.