The morphological characteristics of starch granules preserved on ancient ground stone tools can reveal which plant species were processed and consumed and even infer tool function. Bedrock metates are commonly associated with the processing of localized seasonal resources, providing potential evidence for past human lifeways, including foods collected and processed, social gatherings, settlement patterns, land investment, and territorial behavior. In contrast to ground stone artifacts preserved in a buried context that have been studied extensively, limited starch research has been conducted on the potential for environmental contamination of open-air bedrock mortars and metates exposed to natural erosional elements. This project examines the residue samples of bedrock metates from three archaeological sites in southern Oregon in the United States to compare the starch yields of extraneous material cleaned from the grinding surface to those extracted from interstitial matrices deeper within the bedrock. Significantly greater number of starch granules were recovered from deep within the cracks and crevices than from the surface. Our study suggests that environmental contamination can be managed if separate surface and control samples are collected and analyzed in conjunction with the interstitial samples. Examining the potential for environmental contamination on exposed grinding surfaces is crucial for confidence in starch granule results and improving our understanding of human dietary behavior.

The Paisley Cave archeological site in the Northern Great Basin has provided a rich archaeological record from 13,000 to 6000 cal yr BP, including abundant mammalian coprolites preserved in a well-dated stratigraphy. Here we analyze and contrast pollen from within coprolites and pollen in associated sediments to examine vegetation history and assess whether coprolite pollen provides unique information with respect to the coprolite producer, such as the use of specific habitats, foods, or water sources. We found that the dissimilarity of pollen assemblages between coprolites and associated sediments was greater than the serial dissimilarity between stratigraphically adjacent samples within either group. Serial dissimilarity within types was not greater for coprolites than sediments, as would be expected if there were unique pollen signatures derived from the short period (1–2 days) represented by each coprolite. Compared with sediment pollen assemblages, the coprolites had higher abundances of lighter pollen types, and some individual samples were high in wetland taxa (especially Typha). Our results are consistent with coprolite pollen representing short time periods collected as a mammal moves on the landscape, whereas sediment pollen reflects longer time periods and more regional vegetation indicators.