On the other end, California, with ~39M people gets split into five states: put Hawaii with San Diego for Holiday California; Orange County with rural southern California, for Red California, the LA area would be two states, industrial LA (South), and Hollywood LA (north), and Green California (Norcal/Coast).
California is weird.
Orange County has nothing in common with rural Southern California except a propensity to vote similarly. A big portion of rural Southern California is part of the 909 area code, and in OC referring to someone as being "909" is an insult. Trust me, we don't want them and they don't want us.
You'd be better off putting Orange County with San Diego County. Keep Hawaii. After all, OC can be part of "Holiday California" because we have Disneyland

San Diego County tended to be red in Presidential elections up until about 2008, and is heavily influenced by the military culture.
It's true that LA County people basically think Orange County is San Diego, and SD County people think Orange County is LA, but I think ALL of them would agree that Orange County is nothing like Riverside or Imperial Counties. IMHO Orange County culturally fits better with SD County.
Add Imperial County to Arizona. Add the populated portion of Riverside County (along the I-15 corridor) to the new OC/SD/HI state, or to Industrial LA, and push the rest to Arizona. Add the populated portion of San Bernardino County to Industrial LA and push the rest to Arizona.
Then as you get north of the San Bernardino Mountains and into the Central Valley and high desert, it gets tricky. Most of the high desert areas and the Sierras would probably be fine to add to Nevada.
The Central Valley is probably culturally CA and would fit in a big state encompassing everything from the Central Coast (think anything north of Ventura County) but are farmers who hate the state government and SoCal cities over water rights. That said, including them, along with the Central Coast (lots of farms, wine country), the Bay Area, Sacramento, and then Coastal California north of there including Napa/Sonoma, and some of the farm areas north of Sacramento, could make sense. At least the farmers of the area would all be combined, and would have their interests less diluted than they are today including all of the LA/OC megalopolis and the SD metropolis in their politics.
As you get farther into rural northern California and into southern Oregon, split all that off and shove them in with Nevada as well. They hate Sacramento AND Salem, and hate being dominated by both. These are the "state of Jefferson" people, who may not be happy about being shoved into Nevada, but would be MUCH happier than remaining part of CA/OR.
That's how I'd do it.