California Code, Water Code - WAT § 26502

If any land subject to assessment for the purposes of the district does not appear upon a county assessment roll used as the basis of assessment for the district, the land omitted shall be forthwith assessed by the county assessor of the county in which it is situated upon an order of the board of supervisors making the assessment, and a description of the property omitted shall be written in the roll prepared for the district assessments.