CHRONOLOGY OF THE EVANS CREEK STADE IN SKAGIT VALLEY, WASHINGTON

Recently discovered glacial and lacustrine sediments in the Skagit valley, Washington, provide important new information on the timing and extent of alpine glacier advances during the Evans Creek stade (early Fraser Glaciation). In lower Skagit valley at Cedar Grove, glacial drift overlies an organic bed that yielded a radiocarbon age of 25,040 ¹⁴C yr BP; this age is a maximum limiting date for the Evans Creek stade. Three radiocarbon ages within 100 years of 24,000 ¹⁴C yr BP record damming of upper Skagit valley by the Big Beaver alpine glacier. The ice dam created glacial Lake Skymo, which persisted until at least 18,020 ¹⁴C yr BP, suggesting that Cascade glaciers remained at advanced positions throughout most of the Evans Creek stade. However, growth of a forest on early Evans Creek drift at Cedar Grove 20,730 ¹⁴C yr BP requires at least some recession of the Baker valley glacier. An increase in the number of lowland and montane macrofossils in glacial Lake Skymo sediments at 20,770 ¹⁴C yr BP is consistent with a mid-Evans Creek stade warm interval. Sometime after 20,730 ¹⁴C yr BP, the Baker valley glacier overrode the forest bed and deposited till at Cedar Grove. The advance dammed Skagit River and created glacial Lake Concrete, which persisted until about 16,400 ¹⁴C yr BP.