Green’s Dictionary of Slang

(US Und.) San Quentin prison.

2002		J. Ellroy ‘The D.A.’ in Destination: Morgue! (2004) 146: Ace goes down. Ace gets two years in Big Q.
2007		(con. 1962) in E. Bunker Stark 10: He’s trying to [...] beat the green room at Big Q.