The sport of racing sleds pulled by dogs over snow-covered cross-country courses, dogsled racing, developed from a traditional Eskimo method of transportation. Modern sleds are usually of wood (ash) construction, with leather lashings and steel- or aluminum-covered runners. The dogs used for pulling the sleds are most often Eskimo dogs, Siberian huskies, Samoyeds, or Alaskan malamutes; teams typically consist of 4–10 dogs. The course is usually 12–30 miles (19–48 km) long, though some, including the Iditarod, an annual dogsled race held in Alaska, are considerably longer.