Human Occupation of the Bighorn Mountains

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With National Science Foundation funding, Dr. Robert Kelly will investigate late Pleistocene deposits in caves and rockshelters in northwestern Wyoming. The earliest definitive evidence of human colonization of the North America dates to about 13,200 years ago, the terminal Pleistocene. Unlike later peoples of North America, however, the earliest inhabitants of the continent seem to have rarely used caves and rockshelters. In their colonization model, Robert Kelly and Lawrence Todd (1988) argued that this indicated that the colonizers did not use "rare" landscape elements because they were part of a rapid colonization of North America. However, infrequent occurrence of occupations in caves and rockshelters prior to 12,000 years ago could be a sampling problem (e.g, failure to excavate deep enough), or a result of shelter taphonomy (e.g, shelters that are currently observable were uninhabitable in the late Pleistocene). Understanding how rare the early occupations are is essential to understanding why they are rare. Analysis of data from across the U.S. suggests that early occupations in caves and rockshelters are indeed rare, = 11% of sites with appropriately-aged deposits. Using field data gathered primarily in Wyoming's Bighorn Mts, this projects will adequately sample 12,000-13,500 BP deposits in caves and rockshelters, determine the role of taphonomy in conditioning whether shelters were used, and determine whether the 11% occupancy rate holds true for this region or not. This project investigates a series of shelters from a database of 150 in Wyoming's Bighorn Mountains; currently, only 10-11 of these demonstrate penetration into pre-12,000 year old sediments, and only 2-3 bear evidence of human use in that time range. A sample of 30 shelters with 12,000 - 13,500 year old deposits and that were habitable at the end of Pleistocene will be excavated. The project is primarily re-investigating previously excavated shelters, redating their stratigraphic profiles through AMS radiocarbon and Optically Stimulated Luminescence (OSL) dating to avoid unnecessary excavation of later deposits. With the assistance of two geoarchaeologists the project will collect data relevant to evaluating each shelter's taphonomic and paleoenvironmental history. Test excavations will be conducted in new shelters to ensure acquisition of an adequate sample, as well as an adequate sample of shelters in different bedrock types and settings (e.g. limestone vs. sandstone; high vs. low elevation). Intellectual MeritsOnce completed, this project will (a) establish for the first time, the frequency of terminal Pleistocene occupations in shelters in a specific region; (b) evaluate the probability that sample bias and shelter taphonomy are responsible for the sparse evidence of terminal Pleistocene habitation of caves and rockshelters; and (c) provide data to evaluate one piece of evidence used to support the Kelly/Todd late Pleistocene colonization model. Broader ImpactsThis project (1) enhances training in the University of Wyoming's doctoral program in paleoindian archaeology and enhances international cooperative agreements (a Russian student was sponsored in 2005); in addition, a high school student participated in the project in 2006 (2) compiles information on the archaeological record of Bighorn shelters for other research projects; (3) provides data to help evaluate the utility of OSL dating; (3) is leading to reports/analyses on previously-excavated sites that have not been reported; (4) demonstrates that re-examining previously-excavated sites/collections can have large payoffs; and (5) has helped with public education; for one site, a small museum case was constructed depicting the results of the research; this is now on display at a camp for Los Angeles youth-at-risk on the ranch belonging to the site's landowner.