Earth Notes: Chaco Wood Beams

Sep 28, 2016

Chaco Canyon National Historical Park is noted for amazing structures called Great Houses – massive buildings constructed by the Ancestral Puebloans, who inhabited the nearly treeless high desert of northwestern New Mexico a thousand years ago. Besides local stone and earth, nearly a quarter million trees were harvested for beams in the buildings. 

Chaco wood beams
Credit John Fowler

In a two-pronged study, scientists at the University of Arizona’s Laboratory of Tree-Ring Research compared strontium isotope values in soil and wood to determine the source of the timbers. They matched tree-ring samples collected in the area’s seven mountain ranges with timbers in the Great Houses, comparing and correlating growth patterns to suggest where and when the wood was cut.  

Their conclusion:  most of the spruce and fir was procured from Mount Taylor, 60 miles southeast of Chaco Canyon. But ponderosa pine was the main species used, and much of it probably came from the Zuni Range to the south and from the Chuska Mountains to the west, each about fifty miles from Chaco. The Zuni Mountains also likely supplied most of Chaco’s piñon and juniper. An uptick in ponderosa harvesting in the Chuskas appears to have coincided with an increase in Great House construction during the late eleventh century.

Still unknown is just how the Puebloans moved these large trees such distances to Chaco Canyon.