This is a fascinating place. We spent the day there back in June 98 walking over/through the ruins. For the life of me, I can't figure out why the site was selected to inhabit. You have to wonder how much food could be raised/hunted in this barren area.
I will never forget entering the ruin over a road thru a reservation. We had a rented DeVille and traversed 23 miles of the worst road I can remember -- it took more than an hour to navigate but was worth it. We got there an noticed we were the only vehicle other than an SUV or 4WD. Course, we all know a rent car can go about anywhere. No damage done but was very slow going over a dirt road with rock outcroppings every 100 feet.
I went there in the middle of Summer '93 on a northern road that I believe has since been closed. It took something near 2 hours, IIRC, just driving in on that washboard road. Fun stuff, and great for shaking your fillings loose. ;-D
The north rim of the canyon has quite a lot of bare rock--acres and acres of horizontal surface. It only rains about 8 inches a year there, but when it does rain, all the rain that hits the rock of the north rim runs off. The Chacoans had developed an elaborate irrigation system that was able to capture and channel this runoff, effectively doubling the rainfall available to them during the growing season. Also, there was a dam at the end of Chaco Wash (supposedly a natural sand dune, but I am skeptical)from about 900 AD until about 1020 AD, which raised the local water table quite a bit.
The corn they raised was probably similar to Hopi corn. The Hopi plant their corn very deep...about 8 inches...and the corn has a taproot, which goes very deep for water (unlike most corn, which has a shallow fibrous root system). The Anasazi were able to stretch their meager water resources very far.
Most of Pueblo Bonito appears to be composed of storehouses, which has led some archaeologists to surmise that Chaco was a regional storage and distribution center for the Anasazi, so that when food was plentiful in one area, the excess could be stored there; and when another area was experiencing famine, people could come to Chaco for relief.
Also, many of the plants in that "barren" area are edible. I bought a book on the plants of the Four Corners area, and was amazed to find that the Navajo use almost every one for either food, drink, or medicine.
"I will never forget entering the ruin over a road thru a reservation. We had a rented DeVille and traversed 23 miles of the worst road I can remember -- it took more than an hour to navigate but was worth it. We got there an noticed we were the only vehicle other than an SUV or 4WD. Course, we all know a rent car can go about anywhere. No damage done but was very slow going over a dirt road with rock outcroppings every 100 feet."
Been there, done that. That road was a nightmare.
Climate change. The fact that their settlement changed dramatically around 1300 fits with events in Europe.