The Role of Prehistoric Climate Change in Anasazi Stage Transitions

It seems truly remarkable that temporal stage definitions developed by A.V. Kidder and colleagues at the first Pecos Conference in 1927 have retained much of their vitality for over eight decades and remain in use, with modification, by contemporary Southwestern archaeologists. The underlying reality of why this is so now appears to lie in the punctuated occupational pattern of the southern Colorado Plateau. We have assembled a database of over 27,000 tree-rings dates for the Plateau and adjacent regions. Histograms of these data suggest that the stages of the Pecos classification from Basketmaker III through Pueblo IV represent temporally discrete entities, separated by clear-cut tree-ring minima. We will argue that drought-induced abandonment with significant population relocation to a few favorable Plateau areas, the Rio Grande region and the Mogollon Highlands explains this pattern. In the current paper, we will restrict focus to two drought periods – centered on A.D. 1150 and A.D. 1280 – that gain strong empirical support from Palmer Drought Severity Index modeling. We shall also offer less robust evidence that the earlier stage boundary tree-ring minima were also related to climate. One implication of the study is that the populations that reoccupied the region following major droughts may have been culturally and linguistically unrelated to their local predecessors.