California Code, Government Code - GOV § 9357.2

Any member who rendered service prior to the date he or she became a member may elect, at any time prior to retirement, to contribute to the Legislators' Retirement Fund for each year or fraction thereof for which he or she desires to receive credit for service, a percentage of the compensation received by him or her in respect to that service at the rate prescribed by the provisions of this chapter with respect to his or her service as a member of this system.

Those contributions may be paid by lump sum payment or by installment payments over a period not in excess of the length of time for which the member has elected to receive credit for the prior service, at times and in a manner fixed by the board.  No member shall receive credit for any service for which he or she has not contributed as required by this chapter.