[barney54]

The Clean Air Act allows the federal government to give CA the ability to set alternative standards for car emission controls, but it isn't likely it allows CA to ban all fueled vehicles.

[jdavis703]

They could almost certainly make the price of gas so expensive via taxes that it effectively bans them though.

[larsiusprime]

...aaaand the federal government (via congress, the executive, or the courts) could find some way to intervene and challenge that and hold it up indefinitely.