In 1977, during a BLM wild horse gatherings in a remote area of Beatty's Butte, Oregon, a particular kind of horse was discovered. E. Ron Harding noticed that a number of these horses were similar in color and conformation – they had primitive markings of the Spanish mustangs. Twenty of the primitively marked horses were released in the Kiger herd management area, and seven in the Riddle Mountain herd management area.

Genetic testing by the University of Kentucky revealed Spanish DNA markers in the blood of the Kigers similar to those of the Spanish horses brought to the Americas in the 1600’s. They carry the dominant genes that code for the "primitive dun factor" coloration and markings. Dun factor markings include: dorsal stripe, jack stripe, zebra stripes on legs, arm bars, bi-colored mane and tail, ears with dark outline and fawn colored interior, facial mask and cob webbing.

Kiger’s are not just the light brown dun. They come in many colors carrying the "dun factor." Colors include: dun (a light brown), buttermilk dun, gray, grullo, chestnut, red dun, bay, black, claybank (red) dun, and roan. Some Kiger enthusiasts even recognize a paint with dun factor. The dun markings on all colors are black. The bi-colored mane is usually black or brown highlighted with blond or even red-blond highlights. The Kiger mane is ideally full and long, and falls on both sides of the neck.

The Kiger Mustang is slightly smaller than most breeds and mares from the wild are most commonly large ponies. Stallions can get up to about 15.2 hands. Physical characteristics include: finely pointed ears slightly hooked at the tip, broad, flat forehead, wide, prominent eyes and fine muzzle, wide, deep chest, short back, dense bone, compact hooves, and generally a broad and well muscled stature with a crested "Spanish-style" neck.

Genetically, the Kiger is placed in the light riding breed horse division next to the Iberian horse. The Spanish horse from which the Kiger’s decended were Spanish Barbs bred from Iberians, Andalusians and Berber Arabian horses.

Kiger Mustangs are an established and recognized breed. They are part of a larger group of "Colonial Spanish Horses" recognized by the American Livestock Breeds Conservacy. There are several Kiger registries, the most popular being the Kiger Mesteno Association, the Steens Mountain Kiger Registry and the American Kiger Horse Registry.