Cal. Code Regs. tit. 13, § 1258
All Type 1 school buses and Type 2 school buses constructed on and after July 1, 1970, shall be equipped with two exterior rearview mirrors, one on each side of the bus. Every school bus shall be equipped with a cross-view mirror mounted on the front exterior of the bus to provide the seated driver with a clear view of the area directly in front of the bus.