Cal. Rev. & Tax. Code § 21007

The board shall prepare and publish brief but comprehensive statements in simple and nontechnical language which explain procedures, remedies, and the rights and obligations of the board and taxpayers. As appropriate, these statements shall be provided to taxpayers with the initial notice of audit, the notice of proposed additional taxes, any subsequent notice of tax due, or other substantive notices. Additionally, the board shall include an appropriate statement in the tax booklets which are mailed annually to individuals and corporations. The board also shall include an appropriate statement in the tax booklets informing taxpayers they may be requested by the board to furnish a copy of California or federal tax returns that are the subject of or related to a federal audit.