California Code, Public Resources Code - PRC § 41821.6

In order to ensure that records required pursuant to this article are properly maintained, in addition to inspecting all relevant records, the department may conduct audits, perform site inspections, observe facility operations, and otherwise investigate the recordkeeping and reporting of persons subject to the requirements of this article. Any records, reports, notes, studies, drawings, schematics, photographs, or trade secrets, as defined in Section 3426.1 of the Civil Code, obtained, produced, or created by the department in connection with or arising from those audits, inspections, or observations are confidential and shall not be subject to disclosure under the California Public Records Act (Division 10 (commencing with Section 7920.000) of Title 1 of the Government Code).