California Code, Code of Civil Procedure - CCP § 379

(a) All persons may be joined in one action as defendants if there is asserted against them:

(b) It is not necessary that each defendant be interested as to every cause of action or as to all relief prayed for. Judgment may be given against one or more defendants according to their respective liabilities.

(c) Where the plaintiff is in doubt as to the person from whom he or she is entitled to redress, he or she may join two or more defendants, with the intent that the question as to which, if any, of the defendants is liable, and to what extent, may be determined between the parties.