California Code, Government Code - GOV § 20515

(a) A contracting agency that has included this section in its contract with the board, by express provision or by amendment, on or before December 31, 2001, may provide that, notwithstanding any other provision of this part, service that was in fact also covered under the federal system shall not be deemed as service that was also covered under the federal system, for all purposes of this part, except for the benefits provided by Article 3 (commencing with Section 21570) of Chapter 14.  The amendment shall only be applicable to persons who are employed on and after the effective date of the amendment.

(b) The amendment made to this section by Chapter 636 of the Statutes of 1994 shall apply only to a contracting agency that includes this section in its contract on and after January 1, 1995, and on or before December 31, 2001.