Gov. Code, § 50607

Any objections or protests not made at the time and in the manner provided for by this chapter are deemed waived voluntarily. The validity of proceedings taken under this chapter shall not be attacked subsequent to the hearing upon any ground not stated in an objection or protest filed pursuant to this chapter. Any landowner or person interested in any land within the district is estopped to attack the proceedings upon any ground not stated in a protest filed by him pursuant to this chapter. The validity of the formation of a district formed pursuant to this chapter shall not be contested in any action or proceeding unless the action or proceeding is commenced within 30 days after the time the district is formed. Any appeal from a final judgment in such an action or proceeding must be perfected within 30 days after the entry of the judgment. Any defect, error, or informality in the petition, the clerk’s certificate, the publication, posting, or mailing of notices, or failure of the landowner or person interested in the land to receive notice shall not invalidate any proceeding pursuant to this chapter.