California Code, Revenue and Taxation Code - RTC § 4377

Any delinquent tax roll and original secured roll on which it is based containing the information set forth in the abstract list may be destroyed by the county officer or officers in possession of the rolls if (a) the destruction, in all cases, has first been approved by order of the board of supervisors of the county, (b) the abstract list has first been certified as correct and complete by the county auditor, and (c) a certified, permanent record on a substitute media has been prepared in accordance with Section 26205 of the Government Code and the substitute media will be retained for at least 12 years from the date of the creation of the original document.  The substitute media may also be destroyed following the expiration of the 12-year retention period.

The abstract list prepared under Section 4373, or any photographic record thereof, shall be retained by the tax collector for at least two years after the time the lien has been removed.