Even though the horses can get into the shade, they spend a lot of time in the full sun. Their hides get hot to the touch. But they are tough. As long as they have plenty of water.
I, on the other hand, am not tough. I do not particularly care for summer. Not in Arizona, not anywhere else. One exception: on top of a mountain without any insect pests. The other day I climbed up to a peak at 8780 feet. I sat on top, looked out over miles of Arizona and the edge of New Mexico. The air is thin at that elevation. My pale Caucasian skin was bombarded by radiation. The desert below was baking. On my lofty perch, with a slight breeze, it was 78 degrees. I could have stayed there for hours, alone. But just as I left a troop of 8 hikers who arrived in 4 SUV's arrived to check out the view themselves. I wondered if they were some kind of hiking club. When they returned from the peak trail, they all changed their shoes before driving home. They changed their shoes! I found this terribly amusing. Our society is so specialized that you can't hike and drive in the same footwear. I also thought that they went to a lot of trouble, hiking up the trail to that spectacular view, only to glimpse it briefly and go home. They were not local folks. Local folks would have car-pooled first of all. I don't know. Maybe I am strange. As long as I have plenty of water, I will soak up that sunshine.