Penal Code § 4570
CHAPTER 3. Unauthorized Communications With Prisons and Prisoners
Every person who, without the permission of the warden or other officer in charge of any State prison, or prison road camp, or prison forestry camp, or other prison camp or prison farm or any other place where prisoners of the State prison are located under the custody of prison officials, officers or employees, or any jail, or any county road camp in this State, communicates with any prisoner or person detained therein, or brings therein or takes therefrom any letter, writing, literature, or reading matter to or from any prisoner or person confined therein, is guilty of a misdemeanor.