California Code, Harbors and Navigation Code - HNC § 7037

No informality in any proceeding, including informality in the conduct of the election not substantially affecting adversely the legal rights of any person, shall invalidate the formation of the district.  Any proceedings wherein the validity of the formation of a district is denied shall be commenced within six months from the date of filing of the certified copy of the resolution declaring the district formed with the Secretary of State;  otherwise the formation and legal existence of the district and all proceedings in respect thereto shall be incontestable.