The intent of this study is to analyze the ground stone artifacts (manos and grinding slabs) from 14 late prehistoric sites in the Central Des Moines River Valley of Iowa. This was done to address the relative reliance on maize agriculture during the Moingona Oneota Phase. In total, ground stone artifacts from 11 Moingona Phase Oneota sites were analyzed, as well as ground stone tools from two Middle Woodland sites and one Late Woodland site, for comparative purposes. Based on design theory models and recent research on the correlation between the size and design of ground stone tools and the intensification of agriculture, it appears an overwhelming majority of Oneota manos and grinding slabs are of expedient design. This supports the hypothesis that Moingona Phase Oneota groups were only partially reliant on maize agriculture, with a subsistence base that relied on a mixture of hunting, gathering, and farming.