Correct me if I'm wrong, but I've been under the impression that, by now, California is pretty well recivilized.

Yep California it is but the OP is talking about the Western Half of the Map, its California. The Boarder between California and Nevada runs diagonally right through Nipton.

Its there to give the illusion there is something there, like in FO3 were in the Worldmap the Washington D.C. Ruins were just the building meshes (and a the Obelisk) placed there to give the impression there was something there as Washington D.C. Ruins locations were all separated cells, similar all you see in the distance in FO3 is just there for the illusion.

If I remember O:A worldmap was HUGE because you had the mountains and Anchorage itself but the areas you could actually walk on were much small but the large map had to be done because of the mountain section.

Also if you just open GoogleMaps and look at Las Vegas area you will notice there is really not much there (it is a desert), North there is nothing for miles (besides Area 51) until you reach Alamo (and Area 51 is about west of it), West you have Mt. Carleton, them Pahrump that had a population spike from a population from 2000 in 1980 to 25,000 in 2000 and then Death Valley, East you pretty much have nothing until the Great Canyon and then you have South were you have Bullhead City and the towns around Lake Mohave.

It makes sense for there to be large unpopulated stretches of desert, because we have those now.

I know there is nothing there now but in a future where resorces are gone or running low the need to find more could drive people to those deserts to find new ones. Military bases and other bunkers build to survive a nuclear war would be built there at least by my thinking because its in the ass end of know where. Most survival guides say find a place nowhere close to populated areas. Can't get more unpopulated then Death Valley but like I said in another post one of the main draws of fallout is seeing what has become of real world locations.

They could do a DLC of New Canaan but that's north, not west. There are already references to it in the game.

This guy knows what's up. Fallout universe = different than ours once you're into the 1950's. Could be bunkers, hidden towns, anything. Maybe they built Area 52 there and then the B-3 stealth bomber. All I is saying is that potentially there could be DLC there in the future and i dont see why there shoudlnt be something, however small it is, out there.