Cal. Rev. & Tax. Code § 9257

A certificate by the board or an employee of the board 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 or personal service in accordance with any requirement of this part for the giving of a notice. Unless otherwise specifically required, any notice provided by this part to be mailed or served may be given either by mailing or by personal service in the manner provided for giving notice of a deficiency determination.