Again it goes back to the basic question. The US Constitution is silent on secession; so on that legal ground alone the issue it is up the states. Secession is not legal nor illegal at the Federal level.
The power to regulate states with regard to disposition (admission, size, subdivision, etc) is granted to congress. Authority for question over secession is implied. This is reinforced by SCOTUS decision in Texas v. White.
While it may have been a matter of contention in 1861, it isn’t any longer, sans legal challenges.
No, but there is so much investment in, and sovereignty over, various properties in any given State by the People of the United States (acting through Congress) that a non-consensual secession will eventually have to have recourse to the Laws of War to effectuate its purpose.
In the instant case of California, I do not believe that we, the People of the United States, would willingly surrender our naval basing facilities at San Diego without both proper compensation and a treaty excluding hostile powers in perpetuity. If California decided to take those facilities by force or to prevent their resupply, then California would be exactly where South Carolina found herself in April of 1861.
South Carolina accepted recourse to the Laws of War, indeed appeared for a time to welcome it.
That being the case, the matter of the eleven wayward sisters was rightly settled once and for all at Appomattox.