An interesting article about a very remarkable historical puzzle. Incidentally, the name Anasazi was applied to those Pueblo structures by some local Amerindians, at the end of the 18th century. Charles Babbage published the idea of tree-ring dating in 1837, but the first practical application of it (independently of Babbage, in about 1912) was the dating of the Anasazi structures. The author sensibly comments "Imagine trying to explain the 19th-century Mormon migration to Utah with only tree rings and pollen counts". Jared Diamond gives an interesting study of Anasazi society in his book "Collapse". He points out that the dense and wealthy population of the Pueblos was fed from farms widely scattered outside the canyons, and an enormous number of tree trunks were dragged (by men) over immense distances to build the Pueblo structures. In that arid environment, such a highly stratified social structure was obviously fragile, and it is hardly surprising that a prolonged and severe drought coincided with the abrupt collapse of the entire society. Diamond gives some vivid details of the evidence of the ruling class being eaten in their own homes. The author remarks "Curiously, as was true throughout the region, the victors didn't stay to occupy the conquered lands". But how could they? People living in the canyons depended on food grown at widely scattered farms outside, and some elaborate social structure was required for that food to be supplied to the ruling class living in the canyons.