Cal. Pub. Res. Code § 5517

The notice shall be published once a week for at least three weeks before the day of the election in each municipality in the proposed district. If no newspaper of general circulation is published in any of the municipalities included in the district, the notice shall be posted for at least three weeks in not less than three public places in each of such municipalities. If unincorporated territory is included in the district the notice shall be posted for a like period in at least three public places in the unincorporated territory.