Cal. Water Code § 36455.3

As additional notice a certified copy of any assessment and the diagram attached thereto issued under any of said acts shall be recorded in the office of the county surveyor if the improvement district or any part thereof is in unincorporated territory and with the superintendent of streets of the city or cities if the improvement district or any part thereof is in incorporated territory and shall remain an official record in the office in which it may be filed. Such filing, however, shall not affect or qualify the district record thereof.