Cal. Fin. Code § 6663

If any attachment is levied upon any savings account or any other property maintained with an association or federal association, a copy of the writ and notice of attachment shall be served upon the manager or any other officer of the association or federal association. Service shall be made at the office or branch at which the savings account or other property is maintained, if the office or branch is in operation at the time of the service or, if the office, agency, or branch is not in operation at the time of service, at the home office of the association or federal association. Writs and notices of attachment which are not so served are not effective as to any savings account or other property maintained with the association or federal association, irrespective of any other provision of law relating to service of attachments.