CA Gov't Code Section 110008

On the county implementation date, separate bargaining units shall be created consistent with the bargaining units that have been recognized by predecessor agencies. Bargaining units consisting of employees in a single county shall be the only appropriate unit for collective bargaining under this title. In those counties where no recognized employee organization exists as of the county implementation date, a bargaining unit consisting of all employees in that county shall be deemed an appropriate unit for collective bargaining.