Cal. Water Code § 34308

A finding of the board in favor of the genuineness and sufficiency of the petition and notice is conclusive against all persons except the State in a quo warranto proceeding brought by the Attorney General and commenced before the district has instituted a proceeding to determine the legality of its existence or within one year after the making and entry of the order of the board establishing and describing the boundaries of, and naming, the proposed district if the latter proceeding is not instituted.