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Quaternary stratigraphy and geomorphology of lower Bridge River valley, British Columbia Howes, Don Edwin

Abstract

Bridge River is an east-flowing tributary of Fraser River originating in the Coast Mountains of British Columbia. Its confluence with the Fraser River is near the village of Lillooet. This study encompasses the lower 15 miles (24 km) of Bridge River Valley. The purpose of the study is: (1) to describe and reconstruct the local Quaternary events and relate them to the regional chronology, (2) to produce a surficial geology map, at a scale of 1:50,000. Lacustrine, ice contact fluvio-glacial, fluvio-glacial (lacking ice contact features), glacial, alluvial fan and recent deposits occur here. From their characteristics and stratigraphic relationships, two alternative Quaternary chronologies can be reconstructed: A: Silts and clays deposited in a proglacial lake were subsequently overridden and partly deformed by ice of the last glaciation. Late-glacial aggradation of as much as 400 feet (120 m) of outwash material was succeeded by the fluvial degradation and terracing which continues at present. B: The outwash material represents two phases of proglacial deposition that were preceded by a glacial interval, and separated by the glacial lake phase and the ensuing glaciation. The latter, Chronology B, is favoured. This has been tentatively correlated with the Pleistocene chronology in the adjacent part of Fraser River Valley.

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