True about those folks being tough. I crossed the country from Vermont to Arizoina. And I have always been conservative so don’t worry Az. But thinking about folks that crossed the country on foot, horse back, or in wagons...wow. Those folks were tough. From personal experience I have aclomated to the climate of the areas I have lived in. So the heat isn’t too bad. As long as one stays out of direct sunlight. One late July or early august day some years back, I left work from a location in the desert and the vehicle ambient temperature (outside air) indicated 127F. Now that was hot. But most summer days are less than 110F. And you are so right about dehydration. Bad and it will sneak up on you.
My husband and I lived in Barstow, California, for a year. It's out in the middle of NOWHERE, half way between Los Angeles and Las Vegas. Hot, hot, hot. The area was mostly military and truckers. We could drive to either of the big cities and we did a lot....just to be able to sit in a theater and eat popcorn. Whew! Hot, hot, hot. The 127 is just about normal for the middle of the desert.
Imagine the Bedouins living there in the deserts of the Arabian Peninsula all those thousands of years...it made them what they are: knarly, frowning, abrupt and cranky as heck.
It was as hot as where I lived for FIVE years--Ras Tanura, Saudi Arabia. The hot weather started in mid-April and STARTED to cool down in mid-November. We had ONE day of rain in five years. ONE day.