32,863 Tree-ring Dates Uploaded to tDAR

This post was written by guest author Kyle Bocinsky.

A database of 32,863 tree-ring dates from across the southwestern United States—the largest and most comprehensive of its kind to date—is now available through tDAR. To build the database, we started with a smaller database gathered by Mike Berry and the Dominguez Anthropological Research Group and added several thousand dates from archaeological projects across the Southwest. All dates were determined by the Laboratory of Tree-Ring Research (LTRR) at the University of Arizona. We also used the state site databases for the Four Corners states—Compass (Colorado), NMCRIS/ARMS (New Mexico), Utah Division of State History, and AZSITE (Arizona)—to assign site locations (UTMs) to each tree-ring date.

In an associated research publication—Exploration and exploitation in the macrohistory of the pre-Hispanic Pueblo Southwest (Bocinsky et al. 2016)—my colleagues Tim Kohler, Keith Kintigh, Johnathan Rush, and I analyzed these data for macroscalar patterns, and noted a four-peaked pattern in the number of tree-ring dates through time first established by Mike Berry in the 1980s. These four peaks correspond closely to the widely recognized Pecos classification of Ancestral Pueblo cultural phases. We then compared the tree-ring date distribution to a high-resolution reconstruction of the direct-precipitation maize farming niche across the Southwest from AD 500–1400. We argue that each of the Pecos periods initially incorporates an “exploration” phase, followed by a phase of “exploitation” of niches that are simultaneously ecological, cultural, and organizational. Exploitation phases characterized by demographic expansion and aggregation ended with climatically driven downturns in agricultural favorability, undermining important bases for social consensus. Exploration phases were times of socio-ecological niche discovery and development.

In the research paper, we only use the tree-ring dates from AD 500–1400 (29,311 dates), but we include the comprehensive database in tDAR. We’ve posted two versions of the database: one without site locations that is available to any registered tDAR user, and another available only to those who request permission from Tim Kohler or myself. The database contains site numbers and site names, lab (LTRR) numbers, references where available, the outer date (AD), the outer symbol, and the confidence level. To obtain access to the confidential version with site locations, you must demonstrate that you have permission from the managers of the statewide site files in the four states: Compass (Colorado), NMCRIS/ARMS (New Mexico), Utah Division of State History, and AZSITE (Arizona).

We hope that people find this database useful, and we intend for it to be expanded in the future!



Bocinsky, R. Kyle, Johnathan Rush, Keith W. Kintigh, Timothy A. Kohler, Exploration and exploitation in the macrohistory of the pre-Hispanic Pueblo Southwest, Science Advances 2, e1501532 (2016).

Berry, Michael S., Time, Space, and Transition in Anasazi Prehistory (University of Utah Press, Salt Lake City, Utah, 1982).