Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Radiocarbon ages of midden macrofossils at Chaco Canyon.

In this graph, the y-axis refers to the radiocarbon ages of midden macrofossils at Chaco Canyon. 
The bars represent the number of middens from a given 250-year age range that either do or do not 
contain evidence of pinon pine at the study site. The arrival of pinon pine from its glacial refugium 
in central New Mexico is clearly visible after 9000 14C yr. BP. Pinon is found in all of the middens 
dated between 9,000 and 1,000 14C yr. BP, at which point pinon again drops out of the midden record. 
It is probably not a coincidence that pinon, used intensively as a fuelwood by the Anasazi, dropped 
out of the paleoecological record during the height of Anasazi activity in the Chaco Canyon area.
Although climatic change could partially explain the abandonment of Chaco Canyon by the Anasazi about 
800 years ago, the resident population probably exceeded local carrying capacity even in times of 
optimal weather. An extensive road network connected Chaco with procurement areas of outlying communities, 
but resources close at hand were fully exploited, (Betancourt and Van Devender [1981]). These findings 
have led researchers to speculate that, depletion of fuelwood and other local resources probably intensified 
the reliance on commodity imports from peripheral communities, (Betancourt and Van Devender [1981]).

Indeed, by 1030 A.D., the people of Chaco were forced to rely on logging expeditions to distant mountain 
ranges, sometimes 100 km from home but more typically 30-40 km away, to gather spruce and Douglas fir to 
use as architectural timbers and fuelwood. In the next century, perhaps seeking refuge from the political 
and economic instability that resource depletion engendered, the people of Pueblo Bonito abandoned the canyon 
entirely, moving out to the northern Rio Grande and elsewhere, where their descendants live on in several of 
the Pueblo and Hopi Indian villages of New Mexico and Arizona. 

Photo Credits:
Julio Betancourt 
U. S. Geological Survey