Before 1936, roads from West Yellowstone were not plowed in winter, isolating the town for months. Union Pacific Railroad passenger service reached West Yellowstone only from June into September, and deep snow made winter freight service difficult or impossible; after the town was snowed in, the tracks usually were not cleared until about the end of March. The reopening of the route, known as the Spring Campaign, was celebrated with school dismissed for the day and a grand party marking reconnection to the outside world. During winter, postmasters collected mail every week to ten days from the Sherwood Store near Henry's Lake in Idaho, making the two day round trip over Targhee Pass on skis or by dog sled. In 1933, the first winter air service gave residents a new way to send and receive mail, using a plane fitted with skis so it could land in a snowy clearing, and the pilot also brought milk. Because tourism was the town's main industry, businesses closed for the winter and many residents left for the season, while those who remained shoveled paths, struggled to travel by vehicle, and used skiing and dog sledding to get around and enjoy the snow. A snowplow built in the late 1930s by the Four Wheel Drive Company of Clintonville, Wisconsin, later used by the Montana Highway Department to clear roads in the Gardiner area north of Yellowstone, had a twin-headed engine made by the Waukesha Motor Company in Waukesha, Wisconsin.