California Code, Government Code - GOV § 31639.75

A safety member not previously within the field of membership as a safety member may receive not more than five years of credit as a safety member for all or any part of the time during which he or she was a general member by paying into the retirement fund by lump sum or by installment payments an amount equal to the difference between the member and employer contributions actually made as a general member and the member and employer contributions that would have been made had he or she been a safety member during the time for which he or she claims credit together with regular interest on the amount required to be deposited. A member who elects to receive credit for only a part of his or her county service shall elect that county service latest in time and may not receive credit for any portion of that county service prior in time to any county service for which he does not elect to receive credit. This section is applicable only to active members with five or more years of service as a safety member.

This section applies only to a county of the first class, as defined by Section 28020, as amended by Chapter 1204 of the Statutes of 1971, and Section 28022, as amended by Chapter 43 of the Statutes of 1961.