Those counties that wish to remain in the U.S.A. can become the U.S. State of California, just as the western counties of Virginia became the U. S. State of West Virginia when Virginia seceded from the Union.
The counties in question to remain in the Union should gather, declare themselves to be California, and purge the offending secessionists.
That is kick out LA and San Francisco etc. A congress of 3 representatives from the counties to remain can meet, write the purge declaration and vote on it.
It can be called the Declaration of Purgation.