California Code, Vehicle Code - VEH § 38390

No person shall operate or maintain in a condition of readiness for operation any off-highway motor vehicle which is required to be equipped with a motor vehicle pollution control device under Part 5 (commencing with Section 43000) of Division 26 of the Health and Safety Code or with any other certified motor vehicle pollution control device required by any other state law or any rule or regulation adopted pursuant to such law, or required to be equipped with a motor vehicle pollution control device pursuant to the Clean Air Act (42 U.S.C. 1857 et seq.)  1 and the standards and regulations promulgated thereunder, unless it is equipped with the required motor vehicle pollution control device which is correctly installed and in operating condition.  No person shall disconnect, modify, or alter any such required device.  Notwithstanding Section 43107 of the Health and Safety Code, this section shall apply only to off-highway motor vehicles of the 1978 or later model year.