Cal. Public Utilities Code § 13911

Upon the completion of the annexation of any territory in accordance with law to any city included in the district the city clerk shall file with the secretary of the district a certified copy of the ordinance, resolution or other document completing said annexation, containing a description of the territory so annexed. Unless the district within 90 days after such filing shall file with the city clerk the district’s written objections to the annexation of said territory, or to a specified portion or portions thereof, to the district, said territory, or such portion or portions thereof to which the district does not object as aforesaid, shall upon the termination of said period be deemed incorporated into and annexed to the district, and thereafter is subject to taxation, along with the entire territory of the district in accordance with the assessable valuation of the property thereof, for general district purposes, and for the payment of any indebtedness theretofore or thereafter incurred by the district. Any such objection filed with the city clerk by the district as to a portion or portions of said territory shall describe such portion or portions.