For years the wind blew the sand into the open doorways, through the widening cracks in the walls, past the sealed doorways, down through the floors, until even the deepest and most inaccessible rooms had a layer of 4, 6, or 8 inches of fine sand deposited over them and whatever secrets they held. Rats and other rodents infested the place and little disturbed the brooding silence except for their piping squeals. Occasionally weakened beams gave way or a wall here and there crashed down as its plaster and rubble fill were washed out by rains and melting snows. Bit by bit the old pueblo slowly crumbled. Why and how the first great pueblo was built by a Chaco-like people and then suddenly and for no apparent reason abandoned is a real mystery. Strangely, this abandonment seems to agree roughly with the time at which the Chaco area itself was being depopulated. In Chaco Canyon, an arroyo, much like the one which exists today, was cutting its way backward up the canyon, and this arroyo-cutting would have made it impossible for many of the inhabitants to continue to flood-irrigate their fields. It may have been the basic factor involved in the general abandonment of the great communal dwellings of the Chaco Canyon around A.D. 1150, no doubt coupled with a certain amount of strife and considerable periods of drought. But this would not have been true at Aztec. The Animas River is a perennial stream, and there is no apparent cause for the abandonment of the pueblo by the Chaco-like people, unless for some reason they decided to leave Aztec because the last of their kinfolk in Chaco were leaving that area.