[Steeveedee]

Originally Posted by Chevyland

Well, it all started in late 1971

Yup. It started with cars in the mid-'60s having California-only mandated emission controls. Trucks caught up in the '72 model year. By 1976 the emission controls were all pretty much the same whether a California vehicle or a Federal emissions vehicle. This is why the rolling exemption of vehicles 25 years or older stopped rolling in 2001 in California. Only vehicles of model year '75 and older are now exempt.