Territory which is outside the boundaries of the city, or the initiating city, as the case may be, shall not be annexed unless the governing body of the city within which such outside territory is situated, or, in the case of unincorporated territory, the board of supervisors of the county in which such territory is situated, consents to such annexation by resolution adopted at any time prior to the conclusion of the hearing which is provided for by Section 4646 on the annexation. Any district which as a result of any annexation includes territory not solely within the boundaries of a single city shall thereafter be deemed to be a district formed pursuant to Article 2a (commencing with Section 4614.1) of this chapter even though it was not originally formed pursuant to that article.
Source:
Section 4641.5, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC§ionNum=4641.5..