The Cordilleran Ice Sheet was a massive ice sheet that covered parts of western Canada and the northwestern United States during the last Ice Age, approximately 2.6 million to 11,700 years ago. It extended from the Rocky Mountains to the Pacific Coast, influencing the landscape through glacial erosion and deposition. As the climate warmed, the Cordilleran Ice Sheet began to retreat, leading to the formation of various landforms such as moraines and fjords. Its melting contributed to rising sea levels and shaped ecosystems in the region, impacting both flora and fauna, including species like the mammoth and saber-toothed cat.