This rusted water tower was once used to store water for drinking and fighting fires.
There used to be 6 guard towers on the island. This is the only one that is still standing.
Alcatraz had the first activated lighthouse in the West Coast in 1854. It was damaged in the 1906 earthquake and eventually torned down. When the 600 cell prison was built in 1909, they built a new 84-foot concrete lighthouse which you see here.