San Quentin State Prison (SQ) is a California Department of Corrections and Rehabilitation state prison for men, located north of San Francisco in the unincorporated town of San Quentin in Marin County.Opened in July 1852, it is the oldest prison in California. The state's only death row for male inmates, the largest in the United States, is located at the prison. It has a gas chamber, but since 1996 executions at the prison have been carried out by lethal injection.