On the banks of the Rillito River, this track became the birthplace of many racing innovations still in use today. The Southern Arizona Horse Breeders Association, which pioneered Quarter Horse racing in Tucson, had hosted races at the Hacienda Moltacqua track since 1941. After Moltacqua was sold in 1943, J. Rukin Jelks volunteered the use of the training track on his ranch. Under the direction of Melville Haskell, an American Quarter Horse Hall of Fame inductee, and Van Smelker, who later became head of the AQHA Performance Department, the association experimented with grading races, weighted handicaps, futurities, derbies and stake races, and photo-electric timers. World-famous sprinters such as Shue Fly, Joe Reed II, Piggin String, Hard Twist, Queenie, and Miss Panama all ran there. American Quarter Horses now compete in races around the world and are in demand for showing, ranch work, rodeo, recreational riding, and many other activities, and the AQHA is the world's largest equine breed registry, with its international headquarters in Amarillo, Texas.