Cal. R. 1.21
Whenever a document is required to be served on a party, the service must be made on the party's attorney if the party is represented.
As used in these rules, unless a statute or rule provides for a different method for filing or service, a requirement to "serve and file" a document means that a copy of the document must be served on the attorney for each party separately represented, on each self-represented party, and on any other person or entity when required by statute, rule, or court order, and that the document and a proof of service of the document must be filed with the court.
As used in these rules, "proof of service" means a declaration stating that service has been made as provided in (a) and (b). If the proof of service names attorneys for separately represented parties, it must also state which party or parties each of the attorneys served is representing.
Cal. R. Ct. 1.21