sorry, Geoff, but 5 million Republicans in California have a different opinion.
If California broke off from the USA, within 6 months the Mexicans would invade (not that they haven’t already) and claim at least up thru the central valley. The USA would not defend a hostile California. California would cease to exist except for the northern territory - which would be in constant conflict with both Oregon from the north, seeking to expand influence, and Mexico coming up from the south. The citizenry would live in armed conflict for decades and most would lose their homes and livelihoods. It’s a lose-lose situation. Even a child could figure it out.
Witout water from the USA it would be a wasteland again