Which biome occur in the United States and once contained huge herds of grazing herbivores?

The biome that occurs in the United States and once contained huge herds of grazing herbivores is the grassland biome, specifically the prairies. These vast open spaces were historically home to large populations of bison, elk, and antelope, which thrived on the abundant grasses. Today, while much of the prairie has been converted for agriculture, some areas remain protected as grassland reserves.