The reason people can survive temperatures above 120 degrees in California

The air is very dry here compared to other parts of the country where it is more humid. The primary reason I would say it is dry here is because of all the deserts to the south, and east of places like Los Angeles and San Diego. So, the dryness of the deserts tends to permeate the whole area. So, you don't find really humid places until you go north into Oregon. However, from about San Francisco north on into Oregon is is a little more humid than southern California is.

So, 120 degrees or more Fahrenheit in Palm Springs or Death Valley is survivable if you are prepared for it because of the dryness. But, if it were humid at these temperatures people would just drop like flies because people usually cannot survive very well in 120 degrees or more if there is humidity too.