A series of pollen assemblages and the environments of deposition are shown by samples from 143 levels of interbedded sand, silt, clay, and peaty and woody sediments in sections from the Pleistocene Whidbey Formation at Useless Bay (the type locality), West Beach, Point Wilson, and Foulweather Bluff. Deposition of the formation is interpreted to have taken place over a broad floodplain under fluvial conditions where drainage shifted between and into tracts of paludified ground. Of the four sections studied, only Useless Bay and Point Wilson contain assemblages with analogs found in the modern pollen rain on the floodplains of the Nisqually, Skokomish, and Chehalis Rivers in western Washington, Q-mode factor analysis of pollen percentages in the Whidbey samples extracted Douglas-fir, pine, alder, grass, and sedge as the principals for 93% of the data. Stepwise regression relating modern pollen rain and temperature resulted in a transfer function that, when applied to the principals for the Whidbey, produced mean July temperatures for the intervals represented by the sections. Temperature curves for Useless Bay and Point Wilson show maxima comparable with the modern average of 15.8 °C; maximum values at West Beach and Foulweather Bluff are approximately 2° lower. These curves, when compared with curves from late Quaternary deposits and the "interglacial" Puyallup and Alderton Formations, indicate that sediments belonging to the Whidbey are largely from an interglacial age, comparable to the Holocene or present interglaciation, but also from cooler episodes similar to the late Fraser Glaciation.

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