California Code, Revenue and Taxation Code - RTC § 4946

All or any portion of any uncollected tax, penalty, or costs, heretofore or hereafter levied, may on satisfactory proof submitted by the tax collector be canceled by the auditor on order of the board of supervisors upon a showing that the collection of the delinquent tax can not be enforced because of any errors in description, assessment, equalization, levy, or any other proceeding. If all or any portion of the property was taxable for the year or years for which the cancellation is made, the clerk shall send a notice to the last assessee of the property respecting the cancellation. A similar notice shall be sent to the last assessee, except that the grounds of cancellation need not be stated, in the event that any tax, penalty, or costs, or any portion thereof, is ordered canceled or held void or ordered refunded by a final judgment of a court of competent jurisdiction.