Yeah, the death zones make no sense.
Especially California, like, it's far less densely populated than the East Coast and arguably more fertile, after maybe five or so years of riads and tribalism I don't see how the coastal hills and Central Valley wouldn't have big organized states that arose out of need.
Most of Southern California is wildly overpopulated (even the less-populated rural areas) relative to its potable water resources. That alone is going to cause a massive die off....possibly a clean sweep.
Coastal California is generally densely populated (with a skip of very lightly-populated area above Santa Barbara and below the Bay Area), with three major nodes (LA, San Diego, and San Francisco) that are
definitely going to be utterly destroyed....and take a big swathe of the coastline with them (due to excellent major roads leading North and South along the coast).
The lightly populated areas
with access to water have the opposite problem, ironically. With the population low enough to scrape through (food-, social order-, and water-wise)...you have the danger that the community lacks sufficient division of labor or the right skillsets to prevent a secondary catastrophe (in Oregon and Cali, you need medical personnel to head off the Bubonic Plague, which is endemic in ground rodents in the region, for instance). The communities that survive (like in Oregon, but without Norman doing horrible things that enabled larger immediate Post-Change population clusters) are basically the Goldilocks tale made flesh (not too big, but big enough).
So far,
in canon, we have the Barony of Mist Hills (Mendocino County, somewhere in the hills), and Topanga/Chatsworth (who seem to have survived by forting up and beating off the incoming hordes, and hiding up in the hills and waiting for everyone else to die, respectively).
All things being equal, I would expect a third cluster on the coast (possibly not on the coast-line, though), somewhere in southern Monterey or northern San Luis Obispo counties (very light population density, not too dry, fairly far from LA and SF, etc).
Inland, there's a bunch of places that could carry a community (in terms of food, water, resources, etc).....and the still very coast-bound Montivallans would have not run into them yet (Topanga, Chatsworth, and the Bnei Yaakov have basically
just been contacted in CY 46, and they are all on/near the coast). A Bearkiller-sized state located on the western slope of the Sierra Nevadas would be way off the radar.
Note that a lot of fairly nice locations are going to be empty (or hosting scattered clans of hunter-gatherers)....because the community that might have otherwise made it through intact, just failed to pull it together or succumbed to a disaster ("Things went well for Mayberry. Until the Fire.....").
As to the "Death Zones"...you can't draw a radius around a city and call it a dead zone, as refugees don't radiate out from a common center. They follow the roads and the gradient (staying on major roads, and seldom moving uphill). More realistically, there would be "plumes of Death". Everything on an Interstate or major Highway for a 150km from a major city might be overrun and devastated...but a small bedroom community 50km from downtown Atlanta or Denver, sheltered by a line of low hills (or just no major roads) between it and the big city, might never see a refugee.
