California Code, Revenue and Taxation Code - RTC § 401.16

(a)(1) If the county assessor depreciates this property using percent good factors published by the State Board of Equalization that provide separate factors for property that is first acquired new and property that is first acquired used, the assessor may not average the published factors to apply these factors to both classes of new and used property.

(2) Notwithstanding paragraph (1), if information reported by a taxpayer does not indicate whether this property was first acquired by the taxpayer new or used, the assessor may average the published factors.