California Code, Government Code - GOV § 21034

Public service may be credited as current or prior service, or both, as it would be credited if the member had been in state service during his or her public service. Credit shall not be granted for public service which would be credited as prior service unless the member has contributed for all other “public service” for which he or she is entitled to elect to receive credit as current service with the employer where the prior service is to be credited.

Benefits based on credited public service shall be computed according to the formula determining the member's contribution for that service credit. “Public service,” as defined in subdivisions (a), (b), and (c) of Section 21020 to a member who at membership became subject to a reduced or modified retirement allowance formula because of coordination with the federal system shall be subject to that modified formula to the extent that the service was rendered to any contracting agency in which that modified formula applies after the effective date of coverage under the federal system of members in the employ of that agency.