The day before the buffalo were to be killed, six state livestock agents set out on horseback along Horse Butte to haze the animals that had migrated out of Yellowstone National Park during the night. The herd they were tracking was small, only eighteen head, but up close and streaming through the sage where the butte touched the waters of Lake Hebgen, the buffalo shook the earth and seemed even to shake the water. The horsemen chirped and hiyahed and whistled as they drove the animals into a pine forest. I followed them to the edge of the woods,…