Cal. Public Utilities Code - PUC § 29560. Section 29560.
Upon receipt by the district of a copy of the agreement of annexation properly executed by the district and the county proposed to be annexed the board of directors of the district shall pass a resolution declaring the county annexed to the district, and shall cause a certified copy of the resolution to be filed with the Secretary of State. From and after the date of filing of the resolution with the Secretary of State the annexation of the county to the district is complete.