California Code, Revenue and Taxation Code - RTC § 5805

(a) Notwithstanding any other provision of law,manufactured home accessories, as defined in Section 18008.5 of the Health and Safety Code, installed on a rented or leased lot with amanufactured home first sold prior to January 1, 1977, and which were subject to the state vehicle license fee, shall not be subject to local property taxation, unless themanufactured home is also subject to local property taxation pursuant to this part or the accessory is permanently affixed to the land, such as on a foundation.

(b) In accordance with subdivision (a),manufactured home accessories installed on a rented or leased lot with amanufactured home first sold prior to January 1, 1977, shall be presumed subject to the state vehicle license fee. This presumption may be rebutted by evidence that an accessory was not included in the vehicle license fee base for themanufactured home or was not otherwise subject to the vehicle license fee.