Prospect Hill offered emigrants a delightful view of the Sweetwater mountains, as Amelia Hadley wrote in 1851. Near the first point where westward travelers met the Sweetwater River, Independence Rock stood as an isolated dome of the same composition as the mountains along the valley, its surface polished by ancient winds and carved with many names, leading Father Pierre-Jean De Smet in 1840 to call it the Great Register of the Desert; some sources attribute its name to William Sublette's trading party, which stopped there on July 4, 1830. Six miles west, Devil's Gate formed a dramatic cleft in the granite mountains along the Sweetwater River, so narrow at its base that only the stream could pass through toward the North Platte River, while emigrant trails ran south of it, and early travelers attributed its name to John C. Fremont, who mapped the North Platte and Sweetwater Rivers with Kit Carson in 1842. The Sweetwater River Valley itself was shaped over hundreds of centuries by glaciers, wind, weather extremes, and flowing water, which rounded and wore the granite cliffs and produced sandy soils, and among the visible landmarks along the route of westward migration was Split Rock, whose distinctive outline could be seen for miles and which was first photographed by William Henry Jackson in 1870.