California Code, Code of Civil Procedure - CCP § 872.520

(a) If the name of a person described in Section 872.510 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 872.550.

(b) If the ownership or the share or quantity of the interest of a person described in Section 872.510 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 ownership of the interest had the contingency upon which the right of such person depends occurred prior to the commencement of the action.

(c) The court shall upon its own motion or upon motion of any party make such orders for joinder of additional parties and for appointment of guardians ad litem pursuant to Sections 372, 373, and 373.5 as are necessary or proper.