California Code, Government Code - GOV § 23383

The affected county or counties shall continue to provide necessary services from the date of creation of the proposed county until service responsibilities and functions are transferred to the proposed county according to the provisions of the resolution of the board of supervisors of the principal county adopted pursuant to Section 23369.  The proposed county shall contract with the affected county or counties for such purposes from the date of creation until actual transfer or the effective date or dates for transfer as provided in such resolution.  The contract shall specify the amount or amounts to be paid by the proposed county to the affected county or counties for the performance of such services and functions.  The proposed county may continue to contract with the affected county or counties for any services and functions subsequent to the date or dates specified in any resolution adopted pursuant to Section 23369.