Cal. Sts. & High. Code § 8290

Subject to the provisions of Chapter 8 of Part 1, Division 2, Title 5 of the Government Code, the unincorporated territory of a county which was not included within a district at the time of the formation of such district, and which subsequent to the formation of such district is annexed to or otherwise included within a city which is a part of such district, shall immediately upon such annexation to such city be included within the district and shall thereafter become a part of the district to the same extent as such city; except such portion or portions thereof which the city council has determined, in proceedings under this chapter, will not be benefited by inclusion in the district.