Tuya, a sled dog from Denali National Park, Alaska, stands on the top of her doghouse Jan. 19, 2015. Denali National Park has nearly 30 sled dogs that patrol much of the park’s 6 million acres throughout the winter; visitors are encouraged to meet the dogs while they are not on patrol. (U.S. Air Force photo by 1st Lt. Elias Zani/Released)