Streets and Highways Code § 36521.5

36521.5.

A county may not form an area within the territorial jurisdiction of a city without the consent of the city council of that city. A city may not form an area within the unincorporated territory of a county, without the consent of the board of supervisors of that county. A city may not form an area within the territorial jurisdiction of another city without the consent of the city council of the other city.