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Sand dunes and sand sheets are located along the south side of Kankakee River Valley in Illinois and Indiana, which overlie glaciofluvial outwash, lake sediments, and bedrock of Middle Paleozoic shales and carbonates. Dunes are prominent feature of the landscape, and most dunes are 15 to 25 feet ( ~4-7m) high, and some reach 50 feet (15m). Due to the lack of natural exposure and roadcuts, three dunes were sampled by hand augering for OSL (optically stimulated luminescence) dating. Ground penetrating radar (GPR) surveys were conducted for a better understanding of the stratigraphy where exposures are not available. Results show that all three sites contain ages within the Younger Dryas chronozone (11.5-12.8 ka). More importantly, we found that at site 1 there are about 8 meters of eolian sand yielded 5 ages within the Younger Dryas. Although the large error bar of singular individual OSL age (about 6-9%, about 0.8-1.2 ka) usually does not allow for the determination of a specific climatic event, multiple ages from multiple sites of these dunes and striking thickness in this study all fall into the range of Younger Dryas chronozone. Thus, we believe that the rapid climatic changes before, during and after Younger Dryas play key roles in the dune construction here in the Kankakee River Valley. These changes of the ages are consistent with GPR image and lithology changes observed in the field [ABSTRACT FROM AUTHOR]