Cal. Gov. Code § 25209.6
The board of supervisors may take all necessary action on behalf of the county to participate as a health maintenance organization in Section 1876 of the Social Security Act (Public Law 92-603, Section 226), or Section 300(e) of Title 42 of the United States Code, or any other health maintenance organization provision under Title 18 or 19 of the Social Security Act, or any or all of such provisions, and to provide to its enrollees services in addition to those described in subsection (c), as provided in subsection (g) of Section 1876, including the establishment, receipt, segregation and use of prepayments by and for the benefit of enrollees, execution and performance of contracts, and authorization of the expenditure by the county of whatever funds may be required therefor. In connection with a program under this section, county funds may be expended to provide county supplementation of enrollee prepayment amounts, up to 100 percent of the full prepayment amount for persons or families who, in the judgment of the county, are not financially capable of making the full prepayment.
Ca. Gov. Code § 25209.6