I stopped at Canyonlands NP one time, just passing through. I wasn't prepared for that kind of country or the heat, so I just looked around the area immediate to the campground. Even in my 20s, I recognized a dangerous place when I saw it.
But I grew up in the desert. The guy in the OP was from NC, about as far from desert country as you can get. People just don't realize how dangerous it can be. They don't understand how tiring it can get slogging through deep sand, or how canyons run (or don't), or flash flooding from upcountry when there isn't a cloud in the sky where they are, or sometimes the number of trails that can cause confusion, or the wide temperature swings that can occur in 24 hrs.
But at least he took a fair amount of water with him, which is more than many people do.
Sue