Billings, is city and seat of Yellowstone County, in southern Montana. Located on the Yellowstone River, Billings is the largest city in Montana and the commercial, shipping, and processing center of a region that produces cattle, wheat, and sugar beets. The city is the site of three oil refineries, two large hospitals and related medical services, shopping centers, Eastern Montana College (1927) and Rocky Mountain College (1878). Logan International Airport is the largest in the state. The city functions as a gateway to Yellowstone National Park, the Crow Indian Reservation, Little Bighorn Battlefield National Monument (site of the 1876 Battle of the Little Bighorn), and nearby ski and recreation areas. Points of interest include the city's historic district; several museums of area history; and nearby Pictograph Caves State Monument, with pictographs from four periods of Paleo-Indian, Crow, and Shoshone peoples' occupation. East of the city is Pompey's Pillar, a rock formation with Native American pictographs, that was inscribed by explorer William Clark on July 25, 1806, on the return portion of the Lewis and Clark Expedition (1804-1806). The community, founded in 1882 by the Northern Pacific Railway as a home for its employees, is named for one of the railroad's presidents, Frederick Billings. The railroad's location at the navigable part of the Yellowstone River made Billings an early trading and shipping point. Billings was incorporated as a city in 1885.