A short history of the island:
10,000 years ago a brown valley until the waters eventually ran through leaving the island.
Native Americans called it Rainbow Island. In 1775 Spanish soldiers and priests took the island and renamed it Isla de Alcatraces or Isle of Pelicans. (lot of bird droppings there) 1821-1854 Mexicans drove out the Spanish and then driven out by the US Army. A light house was built to help sailors through the Bay and the island became and American fortress, civil war prison, and in the 20th century a prison for criminals from across the US. In 1963 it lay unused until Native Americans returned where they stayed for 19 months before being expelled. Since 1972 it Alcatraz became part of the Golden Gate National Recreation Area.
You can take tours of the island and many of the grassy areas are being tended to with gardens and the like. I didn't go on the island, just around it.