Cal. Water Code § 55670

If the petition for formation of the zone is signed by owners representing less than 60 percent of the total assessed valuation of the real property within the proposed zone as shown by the last equalized assessment roll of the county, and by less than 60 percent of the taxpayers resident within the proposed zone, as its boundaries shall have been established upon the hearing on the petition, or if for any other reason the board deems it advisable to conduct an election, the board shall by resolution order that a special election be held in the proposed zone to determine whether or not the zone shall be established.