19,000 years ago marks the approximate time when glaciers crossed the present-day Canada–United States border into Western Washington, which is generally considered to be the beginning of the Vashon Glaciation. Cordilleran ice sheet (Wikipedia) The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years. During the Vashon Glaciation, the Cordilleran Ice Sheet grew and advanced southwards at a rate of about 135 metres (443 ft) per year. Hood Canal and the rest of Puget Sound were created about 13,000 years ago, during the Late Pleistocene, by the Puget Lobe of the Cordilleran Ice Sheet. Much of the current topography was formed through the erosion of the depression by the Cordilleran Ice Sheet during the Vashon Glaciation, which lasted from about 19,000 – 16,000 BP. Puget Lobe 
The Skagit River was highly influenced by the repeated advance and retreat of the Puget Lobe of the Cordilleran Ice Sheet. The Vashon Glaciation is an extension of the Fraser Glaciation in which the Cordilleran Ice Sheet advanced south of the present day Canada–United States border into the Puget Sound region. This southern part of the Cordilleran Ice Sheet is called the Puget Lobe. Washington’s Glacial Geology (dnr.wa.gov)
