The entire place under martial law and lockdown?
Gonna be pretty hard given the massive number of homeless
Though, I think these so called “rebels” don’t have much rebellious spirit to begin with, confront them with an ACTUAL authoritarian government and they will follow
If California tried secession then it would be under a Republican President and the Republicans would take the opportunity to forcefully correct California's insanity and make an example.
So yes, the California National Guard would instantly be federalized, the entire state of California would be declared to be in a state of insurrection with its borders closed, the NSA would be ordered to shut down their communications infrastructure, the dams would be closed to shut off water, the surrounding state National Guards would be federalized and ordered deployed to the border crossings with California, all California based banking and financial institutions would be cut off from the rest of the US and the international economy, the US Navy would interdict all shipping too and from California, the USAF would intercept all air travel. The entire state Legislature and Executive (at least everyone who failed to oppose insurrection) would be arrested and stripped of office, California's entire House and Senate delegations would be arrested and stripped of office, any local government officials that expressed support for insurrection would be arrested, every California citizen who signed a petition to that effect, voted for it, or supported it by either force of arms, public endorsement, or financial support would be stripped of their right to vote and fined, any company that supported it or whose leadership supported it would be nationalized, etc.
The state would be
utterly crushed in a matter of days without the federal government hesitating. California would probably be forced to adopt a new Constitution, would absolutely be forced to elect an entirely new slate of elected officials (at all levels), and all those who supported insurrection would be stripped of their right to vote (at the state or federal level) or ever hold office. The balance of power in the House and Senate would also change as the entire California delegation would cease to hold office.
The US decided this issue already, at the cost of ten percent of the nations entire adult male population. Secession is
never going to be allowed to even get off the ground again.