Ever been to a desert at night?
I haven't, and even I know they get cold.
Heck theres Ski resourts within a hours Drive of Vegas.
Thus my point. Basicaly if new vegas was spared the worst of the destruction the reality is that within a year or so you start haveing problems keeping houses warm in winter and cooking food (aparently gas in some form or other was widly avalible given how comom pilot lights are, however given the disruption of the economy created by a "all out" war where everyone was shooting at eachothers citys(and not the actual warplans that both sides in the cold war had. . . IE targeting the other sides nukes,*) whatever was going to thoes pilot lites was not going to last very long. Especialy given the kind of infrastructure you have nowdays to suply gas in the first place (which is also why I go with the "200 months" not 200 years, the bodys of cars sitting out that long would not be rust but dust after 200+ years considering the body of a car is mostly sheetmetal)
* Ironicaly when we showed both Russia and China our "piecuter" charts showing probabl casualies from a "Nuke Vs Nuke strike that specificaly excuded targeting cities, they originaly thought that the US Fatilty estimates were high, in fact they originaly thought we were deliberatly overstating things untill THEIR specialist realised that we were being conservative and assumed that among other factors that all "Neutalised" warheads would be efectivly contained, Just haveing 3 missles hit durring launch would have had the effect of drasticly increasing fatalities from vaporised bomb components that would not reacted but would have captured neutrons and thus radicaly increased the Radiation. For one thing, if another warhead was between 12 and 70% fireballs radius from a 3 MT detonation, the initial low energy neutron pulse from the warhead would have converted between 10-90% of U-238 to U239 then to Np 239 then Pu 239, however long before that point said warhead would be plasma, most assumptions I have seen seem to feel that inside that radius the fireball would "cook off" the nuke, outside that radius the initial neutron pulse was dispersed enough to not triger the chain reaction or to triger a "Fizzle" reaction that would have allowed the warhead to "slow burn". however the Ideal was that each nuke hit would either neutralise the warhead in ground or hit an empty silo. you get the impresion reading some of the old cold war matierial that they were, lets be blunt, mildly nuts on both sides. :facepalm: