The basin occupied by Clearwater Lake was scoured by glaciers during several ice ages, including the Wisconsin Ice Age which ended in this region about 10,000 years ago. The basin subsequently filled with meltwater, but its depth has never been measured reliably. The deepest point is believed to be just east of Diver's Bluff. When Dragon Cone erupted about 8,500 years ago, the lava flowed southwest to the Clearwater River, damming it to a height of and raising the level of existing Clearwater Lake just upstream. This flow is just one example of volcanic activity that has occurred in the Wells Gray-Clearwater volcanic field during the last 500,000 years.