Gov. Code, § 31648

If any officer or employee not previously included within the field of membership of the association is brought within the field of membership or if any elected official chooses to come within the field of membership subsequent to the establishment of the association, he shall not receive credit for service or for prior service unless either (1) he elects to and does pay into the association within one year thereafter, or within such longer time as is provided in the regulations of the board, and before an application for retirement is filed, an amount equal to the contributions he would have made if he had been a member of the association from the date of its organization, or from the date of his entry into county service, whichever is the later, together with regular interest thereon or (2) the governing body, by a four-fifths vote, provides that it shall make, on behalf of all such officers or employees eligible to receive credit for prior service under this section and who so elect subsequent to the effective date of the amendment to this section at the 1963 Session of the Legislature, all or a part of the contributions to the association that the officer or employee would be required to make for his prior service, except that the contributions made by the governmental agency pursuant to this section shall be available only for the purpose of retirement for service or for disability and a member resigning from county service shall be entitled to withdraw only that portion of his accumulated contributions made by him.