Today northwestern New Mexico's Chaco Canyon is a desolate place. Between 900 and 1150 A.D., however, it housed the dazzlingly complex culture of the Anasazi people. Sophisticated agricultural and water control systems, intricate road, trail and signaling networks and monumental architecture made Chaco Canyon the core of their regional hold, which flourished until a 50-year drought brought about its collapse. Understandably then, remains left behind by the early Chaco Canyon dwellers have long captivated scholars. And a study described today in the early online edition of the Proceedings of the National Academy of Sciences has yielded intriguing results.

To construct their prominent, multistoried great housesenormous masonry pueblos, each of which contained several hundred roomsthe Anasazi used more than 200,000 conifer trees. Conventional wisdom holds that because Chaco Canyon itself lacks trees, the builders probably first exhausted nearby timber resources and then turned to trees in the surrounding mountains, located 75 to 100 kilometers away. But an analysis of the strontium isotope signatures in the ancient construction beams and those in living trees from three nearby mountain ranges reveals a different story. Nathan B. English of the University of Arizona and his colleagues found that, in fact, Chaco residents used wood only from some of the mountain ranges early in the construction process, perhaps because of a greater availability of desirable conifer saplings.

Although the three rangesthe Chuska, San Mateo and San Pedro mountainsare equidistant from Chaco Canyon, the team linked the ancient beams to two of the mountain timber sources: the San Mateo and Chuska mountains. This finding, the team writes, "suggests that selection of timber sources was driven more by regional socioeconomic ties than by a simple model of resource depletion with distance and time." That is, the Chaco residents may well have forged relationships with the people living at the base of the Chuska and San Mateo mountains. "The distance and direction of these mountain forests from the canyon," the authors assert, "is a measure of the energy expended to harvest and move timbers, of the organization, ability, and determination of the Chaco Anasazi to build monumental architecture, and of economic, political and social relationships across the San Juan Basin."