Cal. Health and Safety Code § 14920

All or any portion of any such special assessment, penalty or costs heretofore or hereafter entered, shall on order of the board of supervisors be canceled by the auditor if uncollected, or, except in the case provided for in subdivision (e) hereof, refunded by the county treasurer if collected, if it or they were entered, charged or paid: (a) More than once; (b) Through clerical error; (c) Through the error or mistake of the board of supervisors or of the officer, board or commission designated by them to give notice or to destroy the weeds, in respect to any material fact, including the case where the cost report rendered and confirmed as hereinbefore provided shows the county abated the weeds but such is not the actual fact; (d) Illegally; (e) On property acquired after the lien date by the State or by any county, city, school district or other political subdivision and because of this public ownership not subject to sale for delinquent taxes.