Cal. Sts. & High. Code § 8685

If any lot or parcel of land affected by any assessment is not separately assessed on the tax roll so that the installment of the assessment to be collected can be conveniently entered thereon, then the auditor shall enter on the roll a description of the lot or parcel affected, with the name of the owners if known, but otherwise the owners may be described as “unknown owners,” and extend the proper installment opposite the same.