Building an Ancient City

Ancient builders. Scientists have traced the origins of wood used to build dwellings in Chaco Canyon.

A thousand years ago a Native American people, the Anasazi, hauled more than 200,000 pieces of timber from distant mountains to build a city deep in the New Mexico desert. Now, archaeologists are finding that the choice of wood used in the Anasazi dwellings could provide valuable clues about the society. The timber came from two surrounding mountain ranges and not a third equidistant range, suggesting that economic and cultural ties probably dictated the choice of timber sources.

The Anasazi culture dominated what is now New Mexico beginning around 550 A.D. Then, about 850 years ago, the civilization abruptly disappeared, probably because the people dispersed during a prolonged drought. Today the Chaco Canyon remains include 12 wood and sandstone houses, or pueblos. But with three mountain ranges equidistant from the site, the provenance of this lumber has long puzzled archeologists. Some suggest that the Anasazi logged different ranges after exhausting suitable trees from each area, while others argue that their choice of logging site indicates cultural and economic ties with neighboring peoples.

To examine this issue, geochemist Nathan English and his colleagues at the University of Arizona in Tucson compared the chemistry of 52 logs in Chaco's walls with that of 200 log, rock, and water samples in the three ranges. In particular, they measured levels of a rare metal called strontium that has two forms, or isotopes, present in different ratios at different locations. In the 25 September online edition of the Proceedings of the National Academy of Sciences, English's group reports that the lumber came from two ranges--San Mateo and Chuska--that were logged simultaneously. The third mountain range was never touched. These preferences suggest to the researchers that ties to nearby communities determined where the Anasazi logged.

The study not only sheds new light on the wider economic system to which Chaco belonged, but is also a "pioneering" effort to use strontium isotopes to track the origin of botanical remains, says archaeologist Jeremy Sabloff at the University of Pennsylvania Museum in Philadelphia. The researchers are hoping that the new technique will clarify the origin of corn husks and turkey bones at the Chaco canyon.

Related sites

National Park Service Chaco Canyon Web site
Slide shows of Chaco Canyon