With the support of the National Science Foundation, Dr. Ronald H. Towner, colleagues and students will examine the 'old wood' problem in radiocarbon dating of archaeological sites in western Colorado and eastern Utah. The old wood problem is the tendency for radiocarbon (14C) determinations from wood charcoal to be significantly older than the contexts in which the charcoal is found. Five factors can make firewood dates significantly earlier than their archaeological or modern contexts: 1) the tendency of people to use dead wood for fuel; 2) a dead tree or dead branch may have died long before its wood was used for fuel; 3) weathering, decay, or insect activity after tree death can remove many exterior rings and increase the gap between the date of the deadwood remnant and the time of its use; 4) removal of additional exterior rings by burning can further expand the gap; and 5) dating rings from the inner part of the wood's ring series widens the gap still further. Operating singly or together, these processes can produce a gap between date and wood use that exceeds the uncertainty range of radiocarbon dates and thereby seriously overestimate the age of the site involved. This proposed project uses both radiocarbon and tree-ring dating to examine the impacts of 'old wood' procurement on interpretations of the prehistoric and historical period occupations of western Colorado and eastern Utah.

Previous research indicates that the magnitude of the old wood problem varies spatially, environmentally, and perhaps culturally. By collecting abundant samples in three areas along an environmental gradient, the project will assess the impacts of different environments on the age and availability of fuelwood resources. The construction of local multi-species multi-century tree-ring chronologies will be particularly important for dating of Fremont, Gateway Tradition, and Ute sites in western Colorado and eastern Utah, and may be critical in understanding Fremont/Ute relationships and Ute ethnogenesis. This proposed project will help us develop wood use models for the three groups and provide interpretive guidelines for dating the sites. Thus, the intellectual merit of the project is to test environmental variability of radiocarbon dates, create new tree-ring chronologies for the area, develop new models of cultural wood use practices, and evaluate technological change as a factor in radiocarbon dating of sites in these areas.

This project will have broader impacts beyond the Fremont, Gateway Tradition, and Ute archaeology in western Colorado and Eastern Utah. It will make important contributions toward the understanding of radiocarbon dating and wood use practices in arid and semi-arid environments worldwide. The project will also contribute toward graduate and undergraduate student training and development. It may also contribute to calibration other chronometric techniques, such as archaeomagnetism and thermoluminescence dating, and to refining ceramic seriation studies of prehistoric Fremont and protohistoric and early historic Ute pottery types. It will refine models of wood use that may have implications for understanding the impacts of technological change on the exploitation of timber resources.

Project Report

, involved collecting and analyzing wood samples from living trees and dead wood across an environmental gradient on the western slope of Colorado and eastern portions of Utah. Our goals are to determine the age of remnant wood that would have been available to prehistoric and historic period peoples (Fremont and Ute) for use as fuel. Assessing the ages of such wood is critical for determining the relative accuracy of radiocarbon dates from hearth charcoal in different contexts. As part of the project, we also wanted to collaborate with researchers from private industry, federal agencies, non-profit groups, as well as to train students. We collected more than 168 samples from living trees and 238 samples of dead wood from eight locations. Environmentally, our driest sites were near Rifle, Colorado and Price, Utah on the north and the wettest sites were near Paradox and Dove Creek, Colorado on the south. The age of the living trees, and dead wood, have met our expectations, although all the analyses are not yet complete. Drier sites, like Barcus Creek north of Rifle, contain very old trees and dead wood on the ground, whereas wetter sites, like West Paradox Creek, yield younger trees and dead wood. Barcus Creek has living trees with inside rings dating to AD 921 and dead wood with inside rings dating to AD 869. West Paradox, in contrast, has living trees dating to AD 1597 and dead wood dating to AD 1562. These new chronologies have already aided in the absolute dating of samples from Ute wickiup sites—the most endangered site type in Colorado--in several areas of western Colorado, and to dating large "brush" fences that were of unknown ages. The differences in the age of available fuel wood will have profound influence on interpreting radiocarbon dates from sites in the different areas. Our radiocarbon dating of dead wood samples is even more important. One piece of wood, collected in 2010 from Barcus Creek, yielded a radiocarbon date of 2907+-37 years b.p.—almost 3000 years old. The use of such a piece of wood for fuel would drastically skew a radiocarbon date derived from the hearth charcoal by an archaeologist. Additional radiocarbon samples have yielded dates in the 1500s from a site we know from historical photographs was occupied in 1881. We are awaiting more radiocarbon results, but this is just one example of the significance of the research. Our training and outreach have also had very positive and significant results. We have been able to collaborate and train individuals from both private-sector and non-profit groups in the proper tree-ring sample collection techniques. This training has resulted in new collections and new dates from Ute and Anglo sites in the area. Student training has been very successful. One undergraduate learned how to prepare samples and organize a database; one graduate student refined her skills in radiocarbon sample preparation and dating; and one graduate student increased his tree-ring dating skills tremendously. Finally, pubic presentations by the PI and one graduate student were very well received at our national conference.

National Science Foundation (NSF)
Division of Behavioral and Cognitive Sciences (BCS)
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John Yellen
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University of Arizona
United States
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