California Code, Labor Code - LAB § 5955

No court of this state, except the Supreme Court and the courts of appeal to the extent herein specified, has jurisdiction to review, reverse, correct, or annul any order, rule, decision, or award of the appeals board, or to suspend or delay the operation or execution thereof, or to restrain, enjoin, or interfere with the appeals board in the performance of its duties but a writ of mandate shall lie from the Supreme Court or a court of appeal in all proper cases.