Cal. Pub. Resources Code § 5526.1
Any action or proceeding in a district formed pursuant to Section 5506.5, in Sonoma County, in which the validity of the imposition of any tax authorized by this article or the issuance of any bonds under this article or any of the proceedings in relation thereto is contested, questioned, or denied, shall be commenced pursuant to Chapter 9 (commencing with Section 860) of Title 10 of Part 2 of the Code of Civil Procedure. Any such action brought pursuant to Section 863 of the Code of Civil Procedure shall be commenced within 180 days of the levy of the contested tax or the authorization of the bond sale. Otherwise, the taxes and bonds and all proceedings in relation thereto, including the adoption and approval of ordinances, shall be held to be valid and in every respect legal and incontestable.
Ca. Pub. Res. Code § 5526.1