Cal. Code of Civil Procedure § 762.020

(a) If the name of a person required to be named as a defendant is not known to the plaintiff, the plaintiff shall so state in the complaint and shall name as parties all persons unknown in the manner provided in Section 762.060. (b) If the claim or the share or quantity of the claim of a person required to be named as a defendant is unknown, uncertain, or contingent, the plaintiff shall so state in the complaint. If the lack of knowledge, uncertainty, or contingency is caused by a transfer to an unborn or unascertained beneficiary or class member, or by a transfer in the form of a contingent remainder, vested remainder subject to defeasance, executory interest, or similar disposition, the plaintiff shall also state in the complaint, so far as is known to the plaintiff, the name, age, and legal disability (if any) of the person in being who would be entitled to the claim had the contingency upon which the claim depends occurred prior to the commencement of the action.