The modern horse, Equus caballus, evolved on the North American continent but was one of several mammalian species that became extinct here by the end of the Pleistocene epoch some 10,000 years ago. Having survived on the European/Asian continent, the horse was re-established in North America by the Spanish in the 16th century. Escaped horses became known as "mustangs", from the Spanish word "mesteno", meaning "wild". They are also referred to as feral horses since they came from domesticated stock. During the period 1600-1850, mustangs ranged throughout the Great Plains in vast herds, sometimes numbering in the thousands.

The acquisition of the horse by the Plains Indians changed those groups from pedestrian hunter-gatherers to mounted buffalo hunters and warriors within the span of a generation. As saddle stock and cow ponies, these early horses played a significant, even indispensable role in the exploration and settlement of the United States. Their wild kindred figure prominently in the cultural history, art and folklore of the American West.

With the development of the modern ranching era, wild horses came to be regarded as a nuisance to cattlemen and were largely exterminated throughout the West. In the 1950s and 1960s, efforts were begun to preserve wild horses. The 1971 Wild Free-Roaming Horses and Burros Act mandated the protection of these animals as a "national heritage species".

Horses in Theodore Roosevelt National Park do not come under the auspices of the Wild Free-Roaming Horses and Burros Act, but are managed by existing park regulations. For many years the National Park Service attempted to remove all the horses from the park. This policy was reversed in 1970 when the horse was recognized as part of the historical setting. The park now retains a herd of 70-110 animals so that visitors may experience the badlands scene as it appeared during the open range ranching era of Theodore Roosevelt. In order to maintain this population level, the horses are rounded up every few years, and surplus animals are sold at public auction. Today, Theodore Roosevelt National Park is one of the few areas in the West where free-roaming horses may be readily observed.

Wild horses have existed in the badlands of western North Dakota since at least the middle of the 19th century. While ranching near Medora in the 1880s, Theodore Roosevelt wrote:

In a great many--indeed, in most--localities there are wild horses to be found, which, although invariably of domestic descent, being either themselves runaways from some ranch or Indian outfit, or else claiming such for their sires and dams, yet are quite as wild as the antelope on whose domain they have intruded.

Throughout the late 19th and early 20th centuries, cowboys in the Medora area often captured wild badlands horses for use as ranch or rodeo stock. Prior to the establishment of the park in 1947, local ranchers used this area to graze their livestock. A horse round-up held in 1954 removed 200 branded animals. Of the few small bands of horses that eluded capture, several were thought to be the descendants of horses that had run free in the badlands since at least the turn of the century.

Some of the horses in the park do bear a striking resemblance to the types of horses common in this area during the 19th century. As depicted in drawings and early photographs, local horses of that era were typically large-headed, short-backed, and a bit larger than the mustang of the southern Plains. They were often blue or red roans, many having "bald" (white) faces and patches of white on their sides. This color pattern, called an "apron," may be familiar from the paintings of Frederic Remington and C.M. Russell, but is seldom seen in modern horses.

Wild horses typically range in small bands of 5-15 animals, consisting of a dominant stallion, his mares, and their offspring. Frequently a subdominant stallion will "run second" to the leader. Stallions herd their mares by extending their heads and necks low to the ground in a threatening gesture known as "snaking." When a band is in flight, a dominant -mare will take the lead, with the stallion bringing up the rear. Young stallions roam together in "bachelor" groups, sometimes in proximity to a stallion harem.

Once formed, these social groups remain remarkably stable and often range within an established territory. Each such group has an established social hierarchy. Upon reaching sexual maturity at age 2-3, young colts and fillies are driven from their natal group and form new bands. Occasionally a bachelor stallion may try to steal mares from an established group, resulting in fights between rival males. Foals are born in the spring after an 11 month gestation period; this is the only time when the stallions will tolerate the absence of a mature mare from the group.

During the summer months, bands of horses may be seen grazing on the upland plateaus in the southeast section of the park, where they can enjoy the cooling winds and lush grasses. They are often seen along the park boundary from Interstate Highway 94. Herds can also be spotted from the Painted Canyon Overlook or from the top of Buck Hill. While hiking or driving, look for fresh manure to locate horses. Stallions advertise their presence to others by "stud piles." These can frequently be observed along the loop road in the northeast section of the park.

Extreme caution must be exercised in attempting to observe the wild horses closely. Horses have keen senses of smell, hearing, and sight and are extremely wary, often sensing the presence of humans in advance. They are especially fearful of horseback riders. Binoculars are advised for optimal viewing. Please do not chase or harass the horses or attempt to approach them too closely. It is hoped that the sight of free-roaming horses in the badlands landscape will increase the enjoyment of your park visit.