California Code, Health and Safety Code - HSC § 34208

“Area of operation,” in the case of a city authority, includes the city and the area within five miles of its territorial boundaries. It does not include any area which lies within the territorial boundaries of another city unless the governing body of such other city has consented by resolution. It does not include any area which lies within the unincorporated area of any county for which an authority has been authorized to transact business. If a county authority becomes empowered to transact business and exercise its powers, a city authority empowered to transact business and exercise its powers in any of the unincorporated area of the county shall not initiate any further project within such unincorporated territory.