You think the Vietnam anti war protests were bad then wait til you see what happens if the US Army invades CA. The USA will go berserk. Nobody will stop CA if they vote for it. It will be peaceful like when the USSR split up.
The USSR was composed of distict populations with different languages and cultures. Many of the republics had been independent countries- Baltic states, Armenia, Ukraine at various times in the past. CA is diverse, but not to the extent if the USSR.
I don’t think CA could defend itself.
Although a minority there are a considerable number of regular Americans that inhabit the north, the valley and most inland areas. These people would side with the US, just as WVA sided with the union.
Then, the US fleet in SD would control all commerce entering CA ports from the Pacific easily blocking any aid and from the Chicoms.
The metrosexuals from SF and LA are not Johnny Rebs.