Alternate approach:
(only half tongue in cheek)
Have the entire rural east half of the state, simply merge with Nevada...
New Nevada would become a big Republican state, balancing out the electoral votes of the now-smaller leftist California.
Win. Win.
I love almost every idea I’ve heard that splits up California. But in order to get it so that the majority in the state would vote for its passage, you need to come up with something that the millions of socal folks will go for. They are the majority, they won’t vote for something that makes them give up more than they gain.
This won’t be about California alone. The ramifications will have a profound national impact. ;)