Liberals in the rest of the country would be very much against this. Reason being, if you back out vote totals from California from everywhere else_, Trump would have won a comfortable victory in the rest of the country, both in the popular vote aeleelectoral vote.
No way would they want to say bye to California virtually automatic 55 electoral.votes for a Democrat pres. Candidate in the future.
Geographically, most of California is decent. Just carve out a section of coastal malcontents stretching from northern Orange County to northern Marin county and extending as far eastward as Sacramento. Throw a fence around it and call it “Lefty Lunatic Land.”