The single biggest stumbling block for any state to leave the union for any reason is the military. Most of the other problems can be resolved within the borders of the state, but the disposition of existing and theoretical new military hardware, personnel, and bases will always be a sticking point even assuming the federal government and the other states are willing to let them leave.

I mean it’s California. At that point just get a few neighboring states on board, take all the military hardware and shit and be like “Wanna go to war over it?”.