Cal. Government Code § 32341

When the compensation of a member is a factor in any computation to be made under this chapter, there shall be excluded from such computation for any period of service prior to the first day of the month after the effective date of this section, any compensation earned since the establishment of the system upon which compensation the member has not paid contributions into the fund because of the provisions of Section 32322 as it existed prior to October 1, 1949, unless on or before December 31, 1952, such member shall elect by written notice filed with the board to pay into the retirement fund either by lump sum payment or by pay roll deductions over a period not exceeding 36 months, and prior to the effective date of his retirement and thereafter pays into the fund within the period specified such additional amount as he would have contributed as a part of his contributions had Section 32322 always read as it now reads and an amount equal to one-half the additional interest which would have been accrued to his account under such assumptions.