Hi Debbie,
I have read both of your threads--great work! Even with the big hot spot your gardens look very inviting

And, more importantly, it sounds like it brings you much fulfillment.
I have lived in Arizona, and currenly live in very hot Africa, so I know what you're dealing with. I have three main ideas, listed from least to most expensive:
1. Make micro-catchments out of stone and plant mesquite trees in them. They're native, grow fast, and will help create the microclimate that will enable other things.
2. Make microcatchments out of stone, level them with a mixture of sand and compost and plant date palms in them. There is no heat on this earth that date palms can't handle as long as they have water. If you cannot procure any date palms them purchase some tasty dates and plant the seeds in pots. They usually take a month to germinate, less if you soak them for a week first. But I've never had a date pit not germinate. Plant them out when they are a year old.
These first two ideas will take a long time, but that's one of our principles: slow and steady. The third idea can be implemented more quickly...
3. Cover that area with a pergola! In Africa we call it a "hangar". It's posts with cross beams on top. I would cover that with sticks placed side-by-side to create filtered shade underneath. If you can talk to a landscaper, they could probably get you palm branches to cover the top with. And voila, shade! If you added a misting system underneath it then you would have a rain forest climate in which to grow many bananas--and many other things. That's what they do at the Phoenix zoo.
The above ideas notwithstanding, I would really leave you with a friendly suggestion. You mentiona a place near the bottom of the property that is nearly always moist? Go invest your energies there--plant the pistachio trees now! Put the most of your energy into the place that can give the greatest yield. It's called an intensive nucleus. And then build out from there. You will likely be encouraged with the result.