Stratigraphy and chronology of late interglacial and early Vashon glacial time in the Seattle area, Washington

A conformable late Pleistocene sequence of interglacial and glacial sediments in the Seattle area, Washington, can be divided into three units: a lower, unnamed nonglacial unit; a middle unit, the Lawton Clay Member of the Vashon Drift; and an upper unit, the Esperance Sand Member of the Vashon Drift. Radiocarbon dates from the lower unit indicate that the Puget glacial lobe of the Vashon age advanced into the area at some time after 15,000 years ago - several thousand years later than was previously believed.