California Code, Government Code - GOV § 21577

This article shall not apply to any contracting agency nor to the employees of any contracting agency until the agency elects to be subject to this article by amendment to its contract made in the manner prescribed for approval of contracts, except that an election among the employees pursuant to Section 20469 is not required, or, in the case of contracts made after July 20, 1959, by express provision in the contract making the contracting agency subject to the provisions of this article.  Any public agency first contracting with the board on and after January 1, 1994, which has not, pursuant to Section 418 of Title 42 of the United States Code, entered into an agreement with the federal government for the coverage of its employees under the federal system shall be subject to this section.

Except as provided in Section 21578, this article shall not in any event apply to employees of a contracting agency whose services are included in the federal system.  Members who are employees of a contracting agency when the agency becomes subject to this article and whose services are not included in the federal system shall have the right to elect to be subject to this article, that election to be made in the manner, and within the time periods, specified in rules adopted by the board.  Employees of that contracting agency becoming members thereafter shall be subject to this article without election.