Indigenous Peoples of the North American Plains were ecologists of the highest order― then the horse came and changed everything. Beaver, Bison, Horse is an interdisciplinary account of the ecological relationships the Indigenous nations of the Plains had to the beaver, bison, horse, and their habitat prior to contact. Morgan’s research shows an ecological understanding that sustained Indigenous peoples for thousands of years, with critical information on how the beaver manage water systems and protect communities from drought in the Northern Great Plains.