Pronghorn in Yellowstone National Park. The most characteristic large mammal of the Great Plains is the Pronghorn. The Pronghorn was never found outside the High Plains and sagebrush flats of the American West. It is the fastest land mammal in the world and can sprint as fast as 60 mph and can sustain a speed of 30 mph for miles! No other land mammal can keep up with the Pronghorn over a long distance.