I was thinking of having it on a Plateau, my original idea. But of course water would easier to get on the coast, it would be extremely hard to get from any other location. A cave seems like a hard place to build a city, more of a nomad thing. Valley would be ok, but I think Plateau would be best the defend able location, while a coastal city would have an easier start.
Ah, well guess we were thinking alike. Of course, with explaining, it would be possible for the settlers to build some sort of aqueduct, or perhaps dig a well, and get water that way. It's also possible for them to find a nearby lake, or river.
One thing that kept on sticking on was if they are in Texas (Assuming we would be in Texas) would be Oil. It would be a valuable resource, and could be used to power things, and possible get some vehicles running.
Upon second thought, the cars were nuclear powered, unless they came across much older oil consuming vehicles. Still, the oil could be used to power old generators, start fires, and use as a trap/defensive barrier.