Robert Stuart and partners and employees of the fur magnate John Jacob Astor, traveling east in 1812 from the Oregon coast to St. Louis, crossed “a handsome low gap” in the Rocky Mountains in October of that year, after receiving a tip months before about its existence from a Shoshone guide. This marked the discovery by European Americans of South Pass, destined in coming decades to become the main route of American expansion to the West.

As many as half a million people crossed what’s now Wyoming in the mid-19th century before the transcontinental railroad was built. Their trails followed the North Platte and Sweetwater rivers west to South Pass, after which they divided into various routes bound for Oregon, Utah or California. They were making the journey of a lifetime, on routes blazed by Indians and trappers, and then worn deep and wide by thousands of wagons and perhaps millions of draft animals. These trails remain largely unchanged in Wyoming. Their white-topped wagons still hold an important place in the national imagination.

Register Cliff, near present Guernsey, Wyo., is one of three large “registers of the desert” in Wyoming where Oregon-, California- and Utah-bound emigrants carved their names on rock. Many of the inscriptions are from the peak years of Oregon Trail travel in the 1840s and 1850s. The area close to Register Cliff was the first night’s camp west of Fort Laramie. Today, this site is a National Historic Site.