The way that I'd draw the map is to give the People's Republic:
-Mendocino County except for a cluster of rural Republican precincts on the eastern border
-The two main Blue areas of Lake County, connected by a thin strip along a road between them, connecting the eastern one through Lake Berryessa to the southern, Blue areas of Yolo County (including Davis) and connecting that to Sacramento and some adjacent Blue areas on its border.
-All of Sonoma, Marin, San Francisco, San Mateo, and Santa Cruz Counties
-Most of the Blue areas of Napa County (western half to 2/3, basically)
-Vallejo, Benicia, and the blue areas going up the highway to Vacaville (and the city itself) in Solano County (not including Luke AFB, though)
-Contra Costa County, minus most of the rural areas in the central, south central, southeast, and central eastern parts of the county
-Stockton and most of the urban areas continuing south from it and then west, plus a strip of San Joaquin County connecting this area to the northeastern corner of Contra Costa County
-the urban western half of Alameda County, although there's some rural-ish and suburban areas that are in the middle of that area and go into Contra Costa County a bit that may be worth excluding as well
-Santa Clara County except the bulk of the rural Red areas in its eastern 2/5-1/2, with a small strip in the north connecting it to a Blue rural region and a small Blue urban region in Stanislaus County and some of the Modesto area (while avoiding cutting the 99 at that point via PRK territory)
-Hollister and a small rural section connecting it to Santa Clara County
-Most of the urban northwestern third of Monterey County plus a thin coastal strip the rest of the way down to its southern border
-A thin, Blue coastal strip of San Luis Obispo County including SLO itself
-Most of Vandenberg AFB, the Blue urban areas adjacent to it, and a thin coastal strip to the more urban Blue areas in southeastern Santa Barbara County, plus some of the Indian reservation areas just above it
-the majority-Blue cities and adjacent Blue areas in Ventura County (like Thousand Oaks and Ventura), which are mainly along the coast
-Los Angeles County, excluding everything along and north or east of a corridor going from the 57-210-5-Kern County border, as well as most of the area between the 605 and 57, north of the 60, and some adjacent Red areas and some Red areas adjacent to Orange County
-the Blue urban areas of Orange County protruding from urban LA County west/south of the 57/5 corridor and north of the Red coastal areas (it can be reunited with LA County)
-Catalina and most of the other islands off of the coast
The above would preserve a 1/101 corridor connecting LA County to Mendocino County and would constitute the Western or Old California, or what should be called the People's Republic of California.
Everything not mentioned above would be part of the New California, or perhaps it could be styled the Free Republic of California. It preserve most of a 5-57-210-5-99-5 transportation corridor from south to north (as well as one along the 395), with a bypass being possible where the PRK would cut it towards the north. It also provides it with a port in the north (Eureka) and south (San Diego). Some of the aerospace industry is also retained, as are most of the military bases, and also most of the agriculture. This allows for its people to travel through the routes without having to deal with commie State bullshit and laws and also provides economic viability.
There are still enough Blue areas that the government would ideally need to be structured in a way that one legislative house is apportioned in a one county, one senator fashion, which I think could get around Reynolds v. Sims via using indirect election of State Senators. Make the Governor elected by an electoral college reflecting geography with a nod towards population. Make the U.S. Senate primaries be legislative so long as the 17th Amendment remains the law. Disallow plebiscites to create law, for the most part, but keep the veto referendum. If anything requires a popular vote, use a double majority system like what the Swiss use. This would make it very hard for the remaining Blue areas or any one region to dominate the State government. Same for types of areas; urban areas could not dominate, but neither could rural ones. This balance of power would be to everyone's benefit and would also have the happy side-effect of making the State government predominantly Republican.
But this is all a dream at this point. It'd be nice to see, but I don't hold out any real hopes of it ever becoming reality, or anything even close to it.