California is probably the strictest place now for auto emissions.
If you decide to drive around CA for a few months with an out of state license plate, do they stop you now, and tell you to pass CA emissions laws ?
Or if you go for a vacation there, rent an apartment for 3 months, and take your car, how about then ?
If not, it seems like you can still drive a car there for quite some time that is not able to pass CA auto emissions.
Not many older cars can pass those emissions standards, even fairly new cars.