Even the most drought-tolerant tree species need to be "established" before they can survive hot and dry conditions. There isn't really any tree that you can water once when you plant it, then leave it for the summer heat - unless nature is very, very nice.
Getting trees established in West Texas is just hard work - as you can tell by all of the majestic forests surrounding your property.
I would also do the tree planting in the fall. You need the ROOTS to grow in your climate. The air will be cooling in the fall, but the soil will still be warm. Optimum conditions for root growth. What water you are able to get onto the new trees will definitely go farther in the fall.
Arizona cypress is pretty tough if you do manage to get it established.
You might also try some of the woody shrub species (if you like the look). Prairie sumac should fill in nicely in the wetter years if you can get it established past your first drought year.
The TAMU website should have tons of good info on plant selection, planting guides, etc.
Do you go out to the farm "extra" in the fall to hunt quail, clear brush, etc.? I would make my extra trips timed to double-dip on tree care and your other activities.
My farm is 45 minutes from my house. I have hauled a lot of water for newly planted trees. You do need to find a water source near your property where you can fill a plastic tote (or something similar). Either a neighbor, public campground, city supply where the oilfield trucks get freshwater, etc.
I would also recommend keeping a rain calendar for your farm. Nothing will pi** you off more than caring for the trees for 18 months, then having them die in a dry spell where it rained in West Texas, but all of the rain went around your farm and you THOUGHT your trees were good.
Good luck on your tree project.
FishinRod
