From the backstory
The night the name stuck
Platte crossing · Summer 1878
The name came that summer at the Platte crossing. Dry lightning after midnight put three thousand head on their feet and running toward a steep cutbank. The night guard pulled back. Jay put his horse at the point of the run and held there, turning the leaders by lantern light until the herd bent into a mill and wound itself down. In the morning the cook looked the ground over and said the herd had been turned by a man who stood like an old bull bison in the current. The name stuck. Nobody argues with a cook.