I'd think urban populations would tend to be very hard hit -- either in terms of deaths or refugee flow toward places where population density is more in line with available food production with Y2K resources and technology.
If an urban area has nearby agricultural land in quantity that is not dependent on pre-nuke technology/energy to sustain it (i.e. agro-business style irrigation), this would be a mitigating factor (though it certainly doesn't guarantee survival of large populations in and of itself). If the Bay area can remain organized enough (and quite possibly draconian enough) to enforce refugee resettlement policies, I could see it being survivable.
If the area remains organized, however, a big challenge will be the mass flow of refugees from southern California fleeing the Mexican invasion as well as the collapse of food production and water supplies after EMP, fuel shortages, and combat disrupt the flow of water into the area. There's really no direction refugees can go except north -- though how many of them would make it that far is an open question (not much of a drive, but would be pretty rough for most people to do on foot on short or non-existent rations . . .). Of course, refugees from LA and San Diego only have to make it part of the way to collapse food production in communities on the way, creating second order refugees . . .
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