Cal. Health & Safety Code § 19985

If the department determines that standards for the construction of factory-built housing, which have been prescribed by the statutes or rules and regulations of other states, are at least equal to the standards of the State Building Standards Code and the other requirements prescribed by the department, the department may so provide by regulation. Any factory-built housing which a state has approved as meeting its standards for construction shall be deemed to meet the requirements of the department, if the department determines that the standards of that other state are actually being enforced.