Cal. Pub. Util. Code § 16160

If land is annexed to a district, the board shall reestablish the boundaries of the units and election precincts within the district not less than 90 days before any election in the district. The reestablished boundaries shall include the annexed land in the same manner and with the same effect as set forth in Sections 15953 to 15964, inclusive. If land is annexed less than 90 days before an election within the district, the inhabitants of the land included shall not vote at the election.