California Code, Code of Civil Procedure - CCP § 1015

When a plaintiff or a defendant, who has appeared, resides out of the state, and has no attorney in the action or proceeding, the service may be made on the clerk of the court, for that party.  But in all cases where a party has an attorney in the action or proceeding, the service of papers, when required, must be upon the attorney instead of the party, except service of subpoenas, of writs, and other process issued in the suit, and of papers to bring the party into contempt.  If the sole attorney for a party is removed or suspended from practice, then the party has no attorney within the meaning of this section.  If the party's sole attorney has no known office in this state, notices and papers may be served by leaving a copy thereof with the clerk of the court, unless the attorney has filed in the cause an address of a place at which notices and papers may be served on the attorney, in which event they may be served at that place.