Cal. Pub. Util. Code § 1210
If any owner or claimant named in the petition or order on the commission's own motion resides out of the State or has departed from the State or cannot after due diligence be found within the State, or conceals himself to avoid service, or is a corporation having no managing or business agent, cashier or secretary or other officer upon whom summons may be served, who, after due diligence, can be found within the State, and the fact appears by affidavit to the satisfaction of the commission, and it also appears by such affidavit or by the petition or order on the commission's own motion that a cause of action exists against such owner or claimant on whom service is to be made and that he is a necessary or proper party to the proceeding, the commission may make an order that the service be made on such owner or claimant by publication of the commission's order to show cause. The order shall direct that the publication be made in a newspaper designated by the commission as likely to give notice to the owner or claimant to be served, and for such time as the commission finds to be reasonable, at least once a week, but publication against an owner or claimant residing out of the State or absent therefrom shall not be less than two months.
If the address of any owner or claimant as stated in the petition or order on the commission's own motion is out of the State, the secretary of the commission shall, within 15 days after the making and filing of the order to show cause, deposit or cause to be deposited a copy of that order, certified under the seal of the commission, with a copy of the petition or order on the commission's own motion attached thereto or made part thereof, in the United States mail, enclosed in a sealed envelope, registered, with postage prepaid, addressed to such owner or claimant at the address specified in the petition or order on the commission's own motion. Personal service of a copy of the order to show cause and of the petition or order on the commission's own motion out of the State is equivalent to publication and deposit in the United States mail.
Ca. Pub. Util. Code § 1210