Abstract

The character, distribution, and age of the Bridge River ash from postglacial sites in British Columbia and Alberta are discussed. The ash consists of dust-sized shards with ellipsoidal fragments of pumice. With a source in the region of the upper Lillooet River, the ash both, thins and fans out east-northeasterly as far as westernmost Alberta in the vicinity of the North Saskatchewan River. Peat immediately below the ash in a bog near Jesmond, British Columbia, was dated by radiocarbon at 2 440 ± 140 years before present (B.P.). The track of the Bridge River ash overlaps that of the Mazama ash of about 6 600 years, but lies north of the presently known distribution of St. Helens Y ash of approximately 3 200 years B.P. It is suggested that with a distinctive character and limited distribution, the Bridge River ash is potentially valuable as a postglacial marker horizon in southcentral British Columbia.

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