The mid-January snowstorm cleared off overnight. By morning, the temperature had plunged to minus 25 F, and the mountain valley around me was muttering about the cold. Sap deep inside the pine and fir trees had started to freeze hard, making the woodlands creak and pop. The lakes banged and whoomped as their ice cover expanded. Even the air felt brittle, scraping the inside of my throat as I skied hard toward the valley's upper end. I was tracking the male wolverine we called M1. His big paw prints were fresh. He must have come through at dawn. But where was he bound? There was nothing before him but a sheer headwall whose rim marked the Continental Divide, where the snows were far deeper and the temperatures lower yet.