Radiocarbon dates from a conformable sequence of nonglacial deposits indicate that the Purcell Trench was not occupied by ice from at least 43,800 years B.P. until after 25,840 years B.P. This interval coincides with the Olympia Interglaciation. The non-glacial deposits are overlain by till and consist of flood-plain deposits containing wood, peat, and a layer of volcanic ash. These sediments were deposited on a strongly developed paleosol which overlies a second till. Radiocarbon dates from outside the immediate study area are cited as proof that the ice, which deposited the top till, did not advance over the area until after 20,000 years B.P. and had retreated from the Purcell Trench prior to 10,000 years B.P.

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