Cal. SHC § 3012

Any action, suit, or proceeding of any kind or nature in which the validity of any of the proceedings taken under this division is questioned or attacked, and any defense in the action, suit, or proceeding, shall be filed within 30 days after the date of the adoption of the resolution or ordinance finally acting on the investigation report or after the date of final action taken pursuant to Section 2804 or 2808 or Part 7 (commencing with Section 2950). If the action is not brought or a defense is not filed within those 30 days, then thereafter all persons shall be barred in any action, suit, or proceeding from pleading, asserting, or claiming that any of the proceedings up to and including the action on the investigation report, or other action specified in this section, were defective, faulty, or invalid in any respect.