Cal. Health & Saf. Code § 6531
Where an entire district shall have heretofore become located within the boundaries of a city by reason of the incorporation thereof, and said district shall have continued thereafter to function as a sanitary district, and no court having jurisdiction of the subject matter shall have adjudicated that said district has merged with said city, and a portion of the boundary of said district shall thereafter have become extended beyond the territorial limits of said city by reason of annexation thereto, said district shall during all said times be and constitute a legally existing sanitary district and shall not thereafter be deemed or adjudged to have merged with said city by reason of said original inclusion therein.
Ca. Health and Saf. Code § 6531