That, my friends, is a Trans Pecos Rat Snake, or Davis Mountain Rat Snake -- Bogertophis subocularis.
https://en.wikipedia.org/wiki/Trans-Pecos_rat_snake
It is a desert-ish species common down that way. It's nocturnal, which eastern rat snakes aren't.
FWIW, they are pretty docile in the wild and you probably can pick it up without getting bit. Pick up a black rat snake here in Va. you will get bit and slimed by their skunk glands.
Trans pecos generally get pretty big.
If you're worried about poisonous snakes down that way, there are three you have to think about--the copperhead (which ain't all that dangerous, but it turns up a lot), Water moccasins (nasty, big fat beer drinking pit viper with a bad bad reputation that likes to hang out near water-including your pool) and the western diamondback. Coral snakes can turn up too, as can small rare rattlesnakes like the Massasauga and pigmy. Those aren't common though and I think, are endangered...
No, I'm not a know-it-all. Had a collection of snakes--including a trans pecos--when I was in high school. Caught it my self in the Dallas area.
