Actually, I am not sure that Tucson has ever experienced 120 degrees official temperature - I certainly never saw it that hot when during the twenty or so years I was living there. During the hotter periods, temps would often reach 100 degrees, but rarely exceeded 105-106 - which is still plenty hot and requires that you pay attention to what you are doing and watch your internal state very carefully.

Tucson is cooler than Phoenix and the lower desert to the west because it is surprisingly high - about 2500 to 3000 above sea level (Phoenix is about 1000 to 1500 ASL). Altitude is everything in determining temperatures in Arizona.