Cal. Unemployment Insurance Code § 2737

(a) Within 30 days from the date of mailing or serving of the notice of overpayment determination, the person affected may file an appeal to an administrative law judge. The director shall be an interested party to this appeal. The administrative law judge, after affording reasonable opportunity for a fair hearing, shall, unless the appeal is withdrawn, affirm, reverse, modify, or set aside the findings set forth in the notice of overpayment determination. The party and the director shall be notified of the administrative law judge’s decision, together with his or her reasons therefor, which shall be final unless within 30 days from the date of notification or mailing of the decision a further appeal is initiated to the appeals board pursuant to Section 1336. The 30-day period for an appeal to the administrative law judge or to the appeals board may be extended for good cause. (b) “Good cause,” as used in this section, shall include, but not be limited to, mistake, inadvertence, surprise, or excusable neglect. (c) This section shall become operative on March 1, 2018.