California Code, Corporations Code - CORP § 18220

If designation of an agent for the purpose of service of process has not been made as provided in Section 18200, or if the agent designated cannot with reasonable diligence be found at the address specified in the index referred to in Section 18205 for delivery by hand of the process, and it is shown by affidavit to the satisfaction of a court or judge that process against an unincorporated association cannot be served with reasonable diligence upon the designated agent by hand or the unincorporated association in the manner provided for in Section 415.10 or 415.30 of the Code of Civil Procedure or subdivision (a) of Section 415.20 of the Code of Civil Procedure, the court or judge may make an order that service be made upon the unincorporated association by delivery of a copy of the process to one or more of the association's members designated in the order and by mailing a copy of the process to the association at its last known address.  Service in this manner constitutes personal service upon the unincorporated association.