California Code, Revenue and Taxation Code - RTC § 465

(a) Except as provided in subdivision (b), the assessor may destroy any document when six years have elapsed since the lien date for the tax year for which that document was obtained. Documents may be destroyed immediately upon preservation in a medium that provides access to the documents such as microfilm, microfiche, electronic document imaging, or other media that captures a true image of the document that may later be retrieved.

(b) Affidavits claiming an exemption, for the first time, pursuant to Sections 254.5, 257, and 277 may be destroyed by the assessor as follows: