California Code, Government Code - GOV § 9355.5

Membership in this system is exclusive of membership in any other retirement system for state officers and employees. Upon becoming a member of this system, a member ceases to be a member of any other retirement system for state officers and employees of which he or she has been a member. The member is entitled to credit for service rendered prior to membership in this system pursuant to Section 9356.1, but is not entitled to that credit and credit for the same service in any other system.