Salinas Valley State Prison (SVSP) Main Phone: (831) 678-5500. Physical Address: 31625 Highway 101, Soledad, CA 93960 ( Directions) Mailing Addresses. Institution: P. O. Box 1020, Soledad, CA 93960-1020. Inmate Mail: P. O. Box 1050, Soledad, CA 93960-1050. (make sure to include Inmate’s Name and CDCR number as well as last known housing).