Cal. Rev. & Tax. Code § 41144

A certificate by the department or an employee of the department stating that a notice required by this part was given by mailing or personal service shall be prima facie evidence in any administrative or judicial proceeding of the fact and regularity of the mailing of personal service in accordance with any requirement of this part for the giving of notice. Unless otherwise specifically required, any notice required by this part to be mailed or served may be given by mailing or personal service in the manner provided for giving notice of a deficiency determination.