Susanville is a city an county seat of Lassen County, California, USA. At the 2000 census, the population was 13,541. Susanville, a former logging and mining town, is the site of the High Desert State Prison and California Correctional Center. The former prison, a high-security facility, opened in 1995; the latter prison, a minimum-medium security facility, opened in 1963. The prisons and their effects on the community were featured on the PBS documentary. P.O.V..