Cal. Government Code § 31564.5

Whenever the governing body of a district for which the board of supervisors is not the governing body adopts a resolution for the inclusion of such district in the retirement association, if, in the opinion of the board because of conditions peculiar to such district the contributions required from such district by this chapter are insufficient to pay the same proportion of the costs of the system as will be paid by the county, the board may require that such district contract with the board to appropriate additional sums. If, because of conditions peculiar to such district the contributions required from such district by this chapter are greater than necessary to pay the same proportion of the costs of the system as will be paid by the county, the board and such district may contract for lesser sums. Either of such contracts may provide, among other things, that whenever the board of supervisors makes an additional appropriation pursuant to Section 31454.5, the district also will make an additional appropriation calculated by a formula specified in such contract. All such districts are hereby authorized to enter into and perform such contracts.