California Code, Code of Civil Procedure - CCP § 382

If the consent of any one who should have been joined as plaintiff cannot be obtained, he may be made a defendant, the reason thereof being stated in the complaint; and when the question is one of a common or general interest, of many persons, or when the parties are numerous, and it is impracticable to bring them all before the court, one or more may sue or defend for the benefit of all.