Clay mineralogy of late Pleistocene sequences in northwestern Washington and southwestern British Columbia

Pleistocene clay-bearing sediments of parts of northwestern Wash­ington and southwestern British Coliambia were studied in an attempt to determine the clay mineral composition of these units; the origin of these clay minerals; and any correlation between clay mineral composi­tion, sediment type, location, or probable geologic history of the sediments. The Pleistocene stratigraphy of the area is fairly well known, although in some specific locations the stratigraphy has not been determined. Recorded work in the region dates back to Dawson (1887). The units studied range in age from the greater than 50,000 year old Double Bluff Drift to Holocene (Recent) river sediments. The units are composed of silt, clay, peat, gravel, sand, till and glacio- marine drift.