Why did they leave? It is impossible to find a single cause that can
explain it, but there appear to be several that contributed. First, the climate during the Pueblo III period was somewhat unstable with erratic
rainfall patterns and periods of drought. This weather problem climaxed
with a thirty-year drought starting about 1270 that coincided with a
cooling trend that significantly shortened the growing season. Perhaps
the expanding population had pressed the limits of the land's capacity
to support the people so that they were unable to survive the climatic
upheavals of the thirteenth century.