around 1955, and the first race marked the beginning of the Tevis Cup This race was a one-hundred-mile, one-day-long ride starting in Squaw Valley, Placer County, and ending in Auburn. Founded in 1972, the American Endurance Ride Conference was the United States' first national endurance riding association. The longest endurance race in the world is the Mongol Derby, which is long. Breeds In most horse races, entry is restricted to certain breeds; that is, the horse must have a sire (father) and a dam (mother) who are studbook-approved individuals of whatever breed is racing. For example, in a normal harness race, the horse's sire and dam must both be pure Standardbreds. The exception to this is in Quarter Horse racing, where an Appendix Quarter Horse may be considered eligible to race against (standard) Quarter Horses. The designation of "Appendix" refers to the addendum section, or Appendix, of the Official Quarter Horse registry. An Appendix Quarter Horse is a horse that has either one Quarter Horse parent and one parent of any other eligible breed (such as Thoroughbred, the most common Appendix cross), two parents that are registered Appendix Quarter Horses, or one parent that is a Quarter Horse and one parent that is an Appendix Quarter Horse. AQHA also issues a "Racing Register of Merit", which allows a horse to race on Quarter Horse tracks, but not be considered a Quarter Horse for breeding purposes (unless other requirements are met). A stallion who has won many races may be put up to stud when he is retired. Artificial insemination and embryo transfer technology (allowed only in some breeds) have brought changes to the traditions and ease of breeding. Pedigrees of stallions are recorded in various books and websites, such as Weatherbys Stallion Book, the Australian Stud Book and Thoroughbred Heritage. Thoroughbred There are three founding sires that all Thoroughbreds can trace back to in the male line: the Darley Arabian, the Godolphin Arabian, and the Byerley Turk, named after their respective owners Thomas Darley, Lord Godolphin, and Captain Robert Byerly. They were taken to England, where they were mated with mares from English and imported bloodlines. The resultant foals were the first generation of Thoroughbreds, and all modern Thoroughbreds trace back to them. Thoroughbreds range in height, which is measured in hands (a hand being four inches). Some are as small as 15 hands while others are over 17. Thoroughbreds