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.

古代地面石器上保存的淀粉颗粒的形态特征可以揭示哪些植物物种被加工和消耗，甚至推断出工具的功能。基岩金属通常与局部季节性资源的加工有关，为过去人类的生活方式提供了潜在的证据，包括食物的收集和加工、社交聚会、定居模式、土地投资和领地行为。与已被广泛研究的埋藏环境中保存的地面石制品相比，对露天基岩砂浆和暴露于自然侵蚀元素的金属的环境污染潜力进行的淀粉研究很有限。该项目检查了来自美国俄勒冈州南部三个考古遗址的基岩金属残留物样本，以比较从研磨表面清除的外来物质与从基岩更深处的间隙基质中提取的淀粉产量。从裂缝和缝隙深处回收的淀粉颗粒数量明显多于从表面回收的淀粉颗粒。我们的研究表明，如果收集单独的表面样品和对照样品并与间隙样品一起进行分析，则可以控制环境污染。检查暴露的研磨表面的环境污染可能性对于对淀粉颗粒结果的信心和提高我们对人类饮食行为的理解至关重要。