Hart Mountain National Antelope Refuge derives its name from the massive fault block ridge that ascends abruptly nearly three quarters of a mile above the Warner Valley floor in a series of rugged cliffs, steep slopes, and knife-like ridges. The east side of the mountain is less precipitous, descending in a series of rolling hills and low ridges to the sagebrush-grasslands typical of southeastern Oregon and the Great Basin. The rugged diversity of the terrain creates a rich mix of habitat types, home to more than 300 species of wildlife. Featured species include pronghorn antelope, California bighorn sheep, mule deer, sage grouse, and redband trout. The 269,000-acre refuge is one of the most expansive wildlife habitats in the arid West free of domestic livestock. Since its creation in 1936 as a range for remnant herds of pronghorn antelope, management of the refuge has broadened to include conservation of all wildlife species characteristic of this high desert habitat and restoration of native ecosystems for the public's enjoyment, education, and appreciation.