Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico

Abstract

Between A.D. 900 and 1150, more than 200,000 conifer trees were used to build the prehistoric great houses of Chaco Canyon, New Mexico, in what is now a treeless landscape. More than one-fifth of these timbers were spruce (Picea) or fir (Abies) that were hand-carried from isolated mountaintops 75-100 km away. Because strontium from local dust, water, and underlying bedrock is incorporated by trees, specific logging sites can be identified by comparing 87

Prehistoric deforestation at Chaco Canyon?

“…Today Douglas fir grows in isolated parts of the canyon, especially east of the Chaco Core, but spruce did not grow in Chaco during the late Holocene, and therefore some wood must have been imported from higher elevations around the San Juan Basin (4,35,36). One study concluded that the 10 largest ruins in Chaco required ca.…”

“…One study concluded that the 10 largest ruins in Chaco required ca. 45,000 highelevation trees, some from as far as 75 km away, based on species proportions recovered from excavations (37); the standardized size ranges in archaeological specimens indicate selective cutting, which might have forced the Chacoans to find wood in higher, more distant mixed conifer and subalpine forests (11,35,37). Drawing on these arguments, some archaeologists (38) concluded that by the AD 1000s, great house builders procured timber primarily from sources in the Chuska Mountains 80 km to the west.…”

“…Two investigations using strontium isotopes attempted to link architectural timber in Chaco to specific geographic locations outside the canyon (5,35). These studies concluded that a range of tree species were imported to Chaco from distant mountains, most more than 80 km away; limited sampling and the geological complexity of the San Juan Basin made it impossible to identify any individual source with confidence, but the results indicated that at least half the sampled archaeological specimens of ponderosa pine could have grown in Chaco (5).…”

“…1) (5). Despite the recognized problems in the ponderosa pine study related to geological variation and limited sampling, investigators concluded that the strontium isotopic results indicated that the architectural ponderosa used in Chacoan great houses came mostly from the Chuska Mountains to the west and the La Plata and San Juan Mountains to the north (35).…”

“…Because uncertainty is best captured using larger sample sizes, we combined published strontium data from trees reported (5,35) and strontium values from soil and water samples (42) and corrected them to NBS SRM-987 to produce overlapping probability curves ( Fig. 6 and Table S1).…”