Miners during the Alaska gold rush valued dogs primarily for their ability to serve as a method of transportation over snow and ice. Sled dogs, especially Siberian Huskies and Alaskan Malamutes, were essential for hauling supplies and gear in the harsh, frozen terrain. They also provided companionship and sometimes helped with protection against wild animals, but their primary role was in transportation. So, the most accurate reason from the options you provided is:
Dogs were used as a method of transportation over snow and ice.