CCP § 415.95

(a) A summons may be served on a business organization, form unknown, by leaving a copy of the summons and complaint during usual office hours with the person who is apparently in charge of the office of that business organization, and by thereafter mailing a copy of the summons and complaint by first-class mail, postage prepaid, to the person to be served at the place where a copy of the summons and complaint was left. Service of a summons in this manner is deemed complete on the 10th day after the mailing.

(b) Service of a summons pursuant to this section is not valid for a corporation with a registered agent for service of process listed with the Secretary of State.