California Code, Labor Code - LAB § 6611

(a) If the employer fails to appear, the appeals board may dismiss the appeal or may take action upon the employer's express admissions or upon other evidence, and affidavits may be used without any notice to the employer.  Where the burden of proof is upon the employer to establish the appeals board action sought, the appeals board may act without taking evidence.  Nothing in this section shall be construed to deprive the employer of the right to make any showing by way of mitigation.

(b) The appeal may be reinstated by the appeals board upon a showing of good cause by the employer for his failure to appear.