In 1971, wild horses and burros were found roaming across 53.8 million acres of Herd Areas (HAs), of which 42.4 million acres were under the BLM's jurisdiction. Today the BLM manages wild horses and burros in subsets of these HAs, known as Herd Management Areas (HMAs) that comprise 31.6 million acres, of which 26.9 million acres are under BLM management.
The Spring Creek Basin HMA covers more than 20,000 acres in the Disappointment Valley area of southwestern Colorado. Terrain varies from open, rolling hills to rugged mountainous country to the north, south, and east boundaries. Elevation ranges from 6,200 to 7,400 feet.
In the late 1800s, the first horses brought to Disappointment Valley belonged to a Montana rancher. The United States Cavalry used this original ranch stock for their military mounts. In 1940, local residents removed most of the herd, leaving behind a few horses that formed the present day herd.
The HMA is characterized by salt desert shrub community in the valley and pinon-juniper woodland on the slopes and higher elevations. Green rabbitbrush, shadscale, black sage, galleta grass, Indian ricegrass, winterfat, and needle-and-thread grass make up the primary forage items in the horses' diet.
At various times of the year, the HMA provides habitat for elk, mule deer, bald eagles, golden eagles, peregrine falcons, coyotes, prairie dogs, and the occasional black bear and mountain lion. Rattlesnakes are common throughout the HMA.