I wouldn’t be surprised if they just went up the hill to cool off in the summer.
Does the mountain get snow? That was a reliable unpolluted source of water, potentially year around if they captured run off.
The Apaches did that in my home here. Most likely moved up Sierra Blanca just to escape blistering heat and have water.
Yup, could be water supply was better, winds made it cooler, monsoon season didn’t drown everyone, less malaria... ? Or, it was more easily defended from attacks by the none-too-neighborly neighbors.