The goal of this project is to study stream channel erosion that occurred approximately 1000 years ago in the Badlands National Park, South Dakota, northern Great Plains. We believe this erosion was caused by drought during the Medieval Climatic Anomaly (MCA), a period of anomalously warm temperatures between 950 and 1250 AD. While no climate history exists for the Great Plains during the MCA, the effects of the drought are recorded in the landscape throughout the region. In the central Great Plains during the MCA, for example, regional-scale drought reactivated sand dune fields in the Nebraska Sand Hills region. In our study area in the Badlands, the MCA drought is recorded as deeply incised stream channels on the prairie landscape. New in this study is identification of the MCA and drought as factors in landscape development in the Badlands National Park. Natural history guides to the Badlands do not mention the MCA, or drought, as factors in landscape development. Nonetheless, we believe our results are consistent with significant MCA-driven landscape changes. We propose to test the case for this proposed climate link through geologic mapping and radiocarbon analysis of fossil soils (paleosols). Results from the proposed study would contribute to the understanding of the regional and global significance of the MCA, improve the predictive power of climate models for the Great Plains, and contribute to knowledge of the natural history of an important national park.