The Younger Dryas event in earth history provides an important example of a rapid climate change forced by no known external cause. Thus understanding the mechanisms for this change will help to evaluate the internal feedbacks affecting climate. The research outlined in this proposal is important because it will determine the geographic extent of the climatic event in North America. Its scientific approach combines proven and new, experimental methods for precise dating of paleoclimate records and therefore will help to resolve some long-standing and confusing discrepencies in the paleoclimate records of western North America.