Granted that there are considerable forces pushing against splitting the state into two but if the impetus were large enough they would be overcome.
The biggest social and political divide is coastal vs inland which does not lend itself to a very tidy geographic division. Coastal California is liberal, Democratic, highly educated, higher income, created both the computer revolution and biotech, and inland California is uneducated, conservative, Republican, higher poverty, and lives on highly subsidized water for farming. (socialized farming)
The counties with the greatest legitimate complaint are the relatively unpopulated Northern (meaning not in the Bay area) and east of the Sierras. Laws which make sense in areas with millions of people don't make sense there. How can you require the same level of support for 'special needs' students where there are so few that you would have to hire an entire staff for 1 child? And why should some suburban 'bambi' be allowed to regulate the hunting of cougars (who are starting to eat people) and trapping of ground squirrels for people who have a more urgent reason to care about these things?
yrs,
rubato