Cali is the produce capitol of the USA + it has massive crude oil reserves. Trust me Cali would likely succeed from the Union if it could (get away with it, kinda like Alaska).
With 19% below the poverty line (relative to cost of living) California is the poorest state in the nation and just a few decades ago was the richest.
California is experiencing a crushing drought. If they were to secede water flowing into the state could be cut off immediately bringing LA to its knees.
San Diego is a major military base for the US, if California seceded San Diego would be economically ruined.
California has a major portion of their economy in government contracts, all of those would be put under review if California were now a separate country. They might not lose them all but you can imagine that they would lose many.
San Francisco has one of the highest flights from any city in the US based on percentage of the population.
I also suspect that if California were to leave the US that we would see the film industry in the US spring up somewhere else, perhaps Austin Tx, or NY, or even Florida.
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