Cal. Rev. & Tax. Code § 4107

Any redemption certificate may be destroyed by the county tax collector if (a) the destruction has been approved by order of the board of supervisors of the county, and (b) 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 creation of the original document. The substitute media may also be destroyed following the expiration of the 12-year retention period.