Actually, California has the second toughest in the world, if only because Japan doesn't allow changes in emissions as the vehicles get older. Yes, that's right - a ten year old Camry has to pass 2008 specs or else you have to buy a 2008 engine. Joy.
That because Japan has their whole economic structure for automobiles designed around recycling them after a few years. The personal property tax on a car also increases as it gets older in Japan instead of decreasing like is does here. The Japanese governemt also gives tax incentives to buy a new car. That's also why you see so many low mileaged JDM(Japanese Domestic Market) engines available here in the US.