California Code, Water Code - WAT § 72741.2

Any action or proceeding in which the validity of the consolidation of the improvement districts, or of any of the proceedings in relation thereto, is contested, questioned, or denied, shall be commenced within three months from the effective date of the resolution of consolidation; otherwise, the consolidation of the improvement districts and all proceedings in relation thereto, shall be held to be valid and in every respect legal and incontestable.