California Code, Penal Code - PEN § 404

(a) Any use of force or violence, disturbing the public peace, or any threat to use force or violence, if accompanied by immediate power of execution, by two or more persons acting together, and without authority of law, is a riot.

(b) As used in this section, disturbing the public peace may occur in any place of confinement. Place of confinement means any state prison, county jail, industrial farm, or road camp, or any city jail, industrial farm, or road camp, or any juvenile hall, juvenile camp, juvenile ranch, or juvenile forestry camp.