cis2butene

That split has been shifting in the last 20 years or so. When I first became aware of politics the central valley, high desert, inland (southern) valleys, and orange county were red. However, it feels like the rest of the country has been moving right, causing shifts in voting behavior. Some of that is also that califonia is a punching bag for right-wing speeches- similar to how alabama or arkansas is for left-wing speeches.

Riverside/San Bernardino County are now more purple, with larger blue areas. Orange County is more blue on everything except immigration. There are certainly pockets of red left, including much of imperial county, but southern california is looking much more like the bay area in the late 80s than Reagan-era SoCal.

Even central california has blue pockets with the growth of fresno. Fresno county actually went for clinton in 2016 despite solid down-ballot wins for incumbent R reps.

If current trends continue as the state grows in pop (more middle-class people priced out of the major metro areas, growth of secondary metros in logistics/agra hubs like fresno, riverside, and sacramento, and a rise in train commuting) you'll see R areas shrinking to rural areas and areas without good transportation connections. That is a big "if", though, I admit.