I agree that you have it worse down there than we do up north. Those scorching summers must be hell on your trees. Folks in Arizona are much better suited to offer advice to you. All I can really offer is my sympathies.
I’ve got a layer of caliche between 6”-16” below my mediocre topsoil, though it does drain at a somewhat reasonable rate, so I don’t have to punch through it to have a tree grow, but it does lead to shallow rooting in the worst areas of my orchard and certainly does not provide much fertility. Still, my fruit tastes great in seasons I actually get it. Watering is a must. While it isn’t Vegas hot here, we do see high 80’s-90’s with occasional surges into triple digits from mid June through mid September with little precipitation. I’d need to add organic matter mixed three feet deep into my soil—or build a hill accomplishing the same—plus a super thick mulch to get my trees through a summer without irrigation. Maybe I’ll experiment with that setup and a few trees next time I expand the orchard.