Green’s Dictionary of Slang

Rock, the n.

1. [mid-19C] (UK Und.) the prison at Gibraltar, used for transported UK felons.

2. [1930s–70s] (also Big Rock) Alcatraz Federal prison on Alcatraz Island, California.

3. [1950s] (US Und.) Florida State Penitentiary, Raiford.

4. [1960s+] Rikers Island prison, New York City.