ca. 1968 - 1970 I was at the US Army Ordnance Proving Grounds just outside Yuma Arizona. The complaint there was that the increase in irrigation in the area had made it impossible to get enough days hot enough to complete the "Desert Environmental Testing" that was the purpose of the station.

On lots of days in the summer, we'd have to wait until 15:00 in the afternoon to get the 110F needed (still air shade temp), although ground temperatures out in the sun frequently went to 130F or a little more, and vehicle surfaces could hit 165F - 180F.

I did record a couple of 142F still air shade temperatures in the bottom of some gullies - as a research task to see if we could find "local hot spots" to complete some tests.

Interior temperatures in personal vehicles were frequently in the 170F vicinity when you left the office to go back to base.

These conditions were surprisingly "tolerable" IF you had sufficient time to acclimate to them, IF you could appropriately adjust your "workload," and IF you could maintain consistent day-to-day exposure to the heat. The extent of the acclimation can be judged by the instance of the fellow who ran off the road, got stuck in the sand, left his car, and died of exposure when the nighttime temperature dropped all the way down to 68F.

Official post rules required military personnel leaving the post especially during the summer to have a blanket in the vehicle for each occupant; but I don't recall ever being searched on the way out.

John