The Iditarod sled dog race in Alaska

Although the Iditarod sled dog race's precise trail varies annually depending on snow conditions, the 1,000-mile race from Anchorage to Nome often runs through or adjacent to Innoko, Nowitna and Koyukuk National Wildlife Refuges. This photo shows former U.S. Fish and Wildlife Service employee Aliy Zirkle and her dogs run on the frozen Yukon River across the northern part of Innoko Refuge during the 2012 Iditarod.