I'm not sure what the question is.
I've hiked lots in Death Valley, some in Joshua Tree, and some in Anza-Borrego. The best hiking is in the springtime, maybe March 15. After that, you can do it, but it can be intensely hot. If I find myself there in the hot months, I will still hike, but I do it early in the morning, like before dawn until 9 a.m.
I've always found the secret to beating excess heat is to go to higher elevation. Some parks have that, and some don't.
I always wear very thin nylon hiking trousers, a thin synthetic t-shirt, a thin long-sleeve shirt over that, and a baseball cap with a bandana.