Where the herd once roamed through unpopulated wilderness, it now treks from one country to another. This may well be its downfall, for under its calving grounds lies enough oil to keep the United States going for six months. Nowadays in Washington, that’s considered a lot of oil, enough to justify imperilling this venerable herd. Determined to let the world know what will be lost if drilling takes place, Heuer and Allison accompanied the 123,000-strong Porcupine caribou for five months in an uncharted course over mountain ranges, through deep snow, and across semi-frozen rivers. En route, the heavily pregnant caribou and heavily laden humans alike were stalked by wolves and grizzlies newly awake from hibernation — and ravenous.