In 1841 the river (then known as Mary's River) first became the route of the California Trail with the Bartleson–Bidwell Party, later to become the primary land route for migrants to the California gold fields. In 1845 the river was explored by John C. Frémont, who made a thorough map of the region and gave the river its current name. In 1869 the river was used as part of the route of the Central Pacific segment of the Transcontinental Railroad.