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A 20-cm-thick volcanic ash layer at the Palisades along the Yukon River is geochemically correlated with the Old Crow tephra. A buried organic and wood-rich layer above the Old Crow tephra probably records the last interglaciation. The recognition of the Old Crow tephra provides the first chronologic information on the age of the thick sequence of Pleistocene sediments at the Palisades, an important ice-age mammal site in central Alaska and a key locakity for the reconstruction of the history of the Yukon River and the last interglaciation in central Alaska.

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glaucaand P. marianapollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betulazone with increased total pollen influx and very high percentages of Betulapollen, predominantly in the size range of B. nanaand B. glandulosa; and (3) and Alnuszone dominated by Alnuspollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Piceapollen in the Alnuszone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamiferapollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glaucapollen reached 10–15%, indicating the arrival of P. glaucain or near the study area. P. glaucapopulations evidently decreased ca. 8000 yr ago, when Piceapollen percentages and influx fell to low values. About 7000 yr B.P., Alnuspollen percentages and influx rose sharply as alder shrubs became established widely. Piceaonce more expanded ca. 5000 yr ago, but these populations were dominated by P. marianarather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situvegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.