Soils and paleosols were investigated from pre-Reid (early Pleistocene), Reid (Illinoian or early Wisconsinan) and McConnell (classical W.isconsinan) surfaces in central Yukon. Paleosols on the pre-Reid surface indicate that it was subjected to two distinct climates, an initial one which was warm and subhumid with grassland-shrub vegetation and later a more temperate and humid climate characterized by the development of a Luvisol with a red, textural B horizon, in places over 190 cm (75 in) thick. Subsequently, the climate became colder, resulting in the Reid glaciation. Thermal contraction cracks developed in the pre-Reid deposits beyond the limit of Reid glaciation and were filled with eolian sand, as well as minor silt and clay, to form sand wedges. During the subsequent Reid-McConnell interglacial, a cool, subhumid climate prevailed as evidenced by the Brunisolic characteristics of paleosols on deposits of Reid age. This was followed by a cold period which climaxed with the advent of the McConnell glaciation. Sand wedges also formed in the deposits of the Reid glaciation; the wedges are shallower and narrower than those on the pre - Reid surface, suggesting a shorter cold period. During retreatal stages of the McConnell glaciation, a thin blanket of loess was deposited over McConnell, Reid and pre-Reid surfaces, covering the soils on the Reid and pre-Reid surfaces during post - glacial (Holocene) time. Finally, Brunisolic soils developed on the loess blanket and, locally, where the loess is very thin or lacking, on deposits of McConnell age.

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Six distal tephra beds from the Yukon Territory and Alaska have been dated by the fission-track method. Zircon and glass ages were determined for the Fort Selkirk and Lost Chicken tephra beds, but only glass ages for the others.Assuming that no track fading has occurred in the glass, Old Crow and Dawson tephra beds are younger than 120 000 and 52 000 years BP, respectively. Mosquito Gulch tephra is 1.22 Ma old, Fort Selkirk tephra is about 1 Ma old, the Ester Ash Bed is 0.45 Ma old, and the best estimate of the age of Lost Chicken tephra is the range 1.7–2.6 Ma.It is evident from these results and from the known abundance of tephra beds within late Cenozoic deposits of the Yukon Territory and Alaska that application of the fission-track method to distal tephra, in conjunction with detailed characterization studies, offers great potential for elucidation of the late Cenozoic geologic history of Alaska and the Yukon Territory.

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