South Pass, broad, level valley (alt. c.7,550 ft/2,301 m), SW Wyo., cutting across the Rocky Mts. It was used by trappers and explorers before Jedediah Smith inaugurated its use as a route for settlers. An important unit of the Oregon Trail, it served for many years as a gateway for immigration to the west of the Rockies and was later a part of the pony express route.