About the Wild, Free-roaming Horse

Wild horses that roam the American West are feral descendants of domestic stock brought to North America by European colonists during the 1500s. The Spanish or Iberian influence remains very strong in the wild horse populations that have the longest histories of escape from domestication (e.g., the Keiger, Pryor Mountain, and Sulfur Mountain herds have strong Spanish ancestries). Later, however, military, saddle, and draft horses dominated by the Thoroughbred, Morgan, Quarter Horse and draft breeds escaped into the western rangelands or were intentionally released. As their numbers increased, they formed broad zones of introgression (intermixing) with the earlier Iberian colonial bloodlines. These wild horses of mixed ancestry eventually increased to very large populations that now inhabit vast areas of U.S. western rangelands.