So, a quick comment about a proposed California secession:
If it happened it would be an unmitigated disaster. California is a deeply red state outside of its very blue cities. So, sure, let's say the blue urban centers win a referendum on secession.
Immediately, the red counties would tell Congress "we're not with them any more." This has happened before. When Virginia attempted to secede in 1860, the western portion of the state decided not to join that suicide pact and broke off. That's how we got the state of West Virginia.
There are a lot of reasons why rural California would refuse to go along. First, they're highly agrarian and have significant water needs -- so losing access to the rivers flowing into California would be a huge hit for them. (And you better believe the USG would do it, too -- and the citizens of Nevada and Colorado would be cheering at being given California's share of the water allocations.)
Second, look at the electoral results. You'll see a handful of red spots and some weak blue spots. These are not counties predisposed to sign onto what they consider "progressive nonsense from San Francisco".
So -- the western edge of California secedes; everything more than 100km inland refuses to go along.
Now for the pain.
Secession proponents like to talk about how California is a wealth-generating machine -- and it is! Cities are economic powerhouses in the general case, and Secessionist California has a lot of them. But look at how cities generate that wealth: they overwhelmingly due it by processing raw materials from rural America. Rural America is vast and bountiful but produces few finished goods; urban America is small and phenomenally good at the task of adding value to the resources it receives from the rural areas...
... you know, the rural areas which have just invited massive numbers of federal troops to come in, in order to stave off Secessionist California occupying them by force in order to ensure the resources flow.
Resources *stop flowing* from rural CA to the cities. They now flow east to Nevada.
So, already, the CA economic powerhouse -- and it is a powerhouse, I want to give it proper credit -- gets derailed by losing the resources it's dependent on. And that's a huge problem, because they now have what is conservatively an immediate $50 billion infrastructure task:
Thirty seconds after Loyalist CA refuses to join Secessionist CA, the federal government rewards Loyalist CA by not only letting them keep their water allocation, but SHUTTING OFF WATER TO LOS ANGELES.
Four million Angelenos now have an urgent task: don't die of dehydration in the first week of secession. Secessionist CA government begins a crash program of building desalinization plants (none of which would be ready for months), and serving Los Angeles with 40 million liters of drinking water each day.
Keep in mind that you can't drink ocean water. Secessionist CA will be forced to buy drinking water, in huge quantities, and then distribute it to cities.
How quickly do you think they could get that program operational and running at full capacity?
Remember: after three days Angelenos will be drinking their own urine to survive. After five they'll be dead. Given how fast the California Legislature acts, I think there'd be over a million dead before the Secessionist Legislature finished buying chairs for the conference room.
The prospect of the USG shutting off water to Los Angeles is literally horrifying. It is so beyond-awful that if one nation were to do it to another, it would be called a war crime. But international norms are very quiet about civil wars.
Go ahead: ask the citizens of Atlanta or Savannah what their experiences were like. Ask them how Abraham Lincoln treated cities in rebellion.
The idea of a secessionist California succeeding is the political equivalent of a Monty Python sketch -- it's so implausible and surreal that it entertains. But just as the How Not To Be Seen sketch, if done in real life, would immediately result in a lot of people with guns swarming the scene and terrible consequences for all, a California secession, if done in real life, would ... do the exact same thing.