California Code, Revenue and Taxation Code - RTC § 261

(a) Except as otherwise provided in subdivisions (b) and (c), as a prerequisite to the allowance of either the veterans' or welfare exemption with respect to taxes on real property, the interest of the claimant in the property must be of record on the lien date in the office of the recorder of the county in which the property is located.  Failure of the claimant to establish the fact of such recordation to the assessor constitutes a waiver of the exemption.

(b) A claimant for the veterans' exemption who on the lien date has an interest in real property consisting of an unrecorded contract of sale may in lieu of the recordation pursuant to subdivision (a) furnish or show the contract to the assessor and file an affidavit with the assessor stating all of the following:

(c) A claimant for the welfare exemption which on the lien date has a possessory interest in publicly owned land, owns water rights, or owns improvements on land owned by another may in lieu of the recordation pursuant to subdivision (a) file a copy of the document giving rise to that possessory interest or water rights or file a written statement attesting to the separate ownership of those improvements with the assessor.  That document copy or written statement shall not be required annually following the year in which it has been filed but shall remain in effect until such time as that possessory interest terminates or ownership of the water rights or improvements transfers.