Iditarod Trail Sled Dog Race early in the 20th century. The main route of the Iditarod trail extends from Seward in the south to Nome in the northwest, and was first surveyed by Walter Goodwin in 1908, and then cleared and marked by the Alaska Road Commission in 1911 and 1912. The entire network of branching paths covers a total of . Except for the start in Anchorage, the modern race follows parts of the historic trail. The trail is composed of two routes: a northern route, which is run on even-numbered years, and a southern route, which is run on odd-numbered years. Both follow
Iditarod Trail Sled Dog Race reveals the results of tests on the dogs. Each team is composed of twelve to sixteen dogs, and no more may be added during the race. At least five dogs must be on the towline when crossing the finish line in Nome. Mushers keep a veterinary diary on the trail and are required to have it signed by a veterinarian at each checkpoint. Dogs that become exhausted or injured may be carried in the sled's "basket" to the next "dog-drop" site, where they are transported by the volunteer Iditarod Air Force to the Hiland Mountain Correctional Center at Eagle River