During the last two million years, dramatic shifts in climate brought long cold periods that lasted thousands of years, as accumulating snow formed ice sheets that spread across most of Canada and the northern United States. The last great episode of the Ice Age, called the Wisconsin Glaciation, ended about 10,000 years ago and radically altered this landscape by excavating vast quantities of rock and soil and then depositing debris as the ice melted to create a wide variety of glacial features. Ice Age National Scientific Reserve preserves evidence of these great glaciers at nine sites administered by the Wisconsin Department of Natural Resources in cooperation with the National Park Service so present and future generations may study and enjoy their glacial inheritance. Although the glaciers of the most recent Ice Age never reached Mill Bluff, their meltwaters did, damming drainage channels just north of Devils Lake and backing up into Glacial Lake Wisconsin, where Mill Bluff stood as an island above the lake.