Westward expansion In the 19th century, pioneers heading West needed a hardy, willing horse. On the Great Plains, settlers encountered horses that descended from the Spanish stock Hernán Cortés and other Conquistadors had introduced into the viceroyalty of New Spain, which became the Southwestern United States and Mexico. The horses of the West included herds of feral animals known as Mustangs, as well as horses domesticated by Native Americans, including the Comanche, Shoshoni and Nez Perce tribes. As the colonial Quarter Horse was crossed with these western horses, the pioneers found that the new crossbred had innate "cow sense", a natural instinct for working with cattle, making it popular with cattlemen on ranches. Development as a distinct breed Early foundation sires of Quarter horse type included Steel Dust, foaled 1843; Shiloh (or Old Shiloh), foaled 1844; Old Cold Deck (1862); Lock's Rondo, one of many "Rondo" horses, foaled in 1880; Old Billy—again, one of many "Billy" horses—foaled circa 1880; Traveler, a stallion of unknown breeding, known to have been in Texas by 1889; and Peter McCue, foaled 1895, registered as a Thoroughbred but of disputed pedigree. Another early foundation sire for the breed was Copperbottom, foaled in 1828, who tracks his lineage through the Byerley Turk, a foundation sire of the Thoroughbred horse breed. The main duty of the ranch horse in the American West was working cattle. Even after the invention of the automobile, horses were still irreplaceable for handling livestock on the range. Thus, major Texas cattle ranches, such as the King Ranch, the 6666 (Four Sixes) Ranch, and the Waggoner Ranch played a significant role in the development of the modern Quarter Horse. The skills required by cowboys and their horses became the foundation of the rodeo, a contest which began with informal competition between cowboys and expanded to become a major competitive event throughout the west. The Quarter Horse dominates in events that require speed as well as the ability to handle cattle. Sprint races were also popular weekend entertainment and racing became a source of economic gain for breeders. As a result, more Thoroughbred blood was added into the developing American Quarter Horse breed. The American Quarter Horse also benefitted from the addition of Arabian, Morgan, and even Standardbred bloodlines. In 1940, the American Quarter Horse Association (AQHA) was formed by a group of horsemen and ranchers from the Southwestern United States dedicated to preserving