From the website:
Welcome to the Spanish Mustang Registry. The Spanish Mustang helped shape the USA. Descended of the horse of the Conquistadors, Indian buffalo hunters, war ponies, cavalry mounts, Pony Express ponies, and wild horses, this breed has a rich and illustrious history that forms an important part of our American heritage. Read more on our site about the history of the Spanish Mustang, find horses for sale, and more.