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.