Cal. Gov. Code § 19586
Within 30 days after the day a copy of the decision rendered by the board in a proceeding under this article is served by the board upon the parties to the decision, either party may petition the board for rehearing of the decision. The petition for rehearing shall be in writing and shall contain all of the grounds upon which a rehearing should be granted.
Within 30 days after the filing of a petition for rehearing with the board, the board shall cause notice thereof to be served upon the other parties to the proceeding by mailing to each a copy of the petition for rehearing. The other parties to the proceeding shall have 20 calendar days from the date of service of a copy of the petition for rehearing to file with the board and serve upon the petitioner a response to the petition for rehearing.
Within 90 days after service of notice of filing of a petition for rehearing, the board shall either grant or deny the petition in whole or in part. Failure to act upon a petition for rehearing within this 90-day period is a denial of the petition.
Ca. Gov. Code § 19586