Interstate 15 follows the latest in a long line of routes through this area that date back to prehistory. Native Americans used this corridor for generations, and its first recorded use came when the Lewis and Clark Expedition passed through on August 10, 1805, naming cliffs north of here for the many rattlesnakes they encountered while traveling upriver. After gold was discovered at nearby Grasshopper Creek and Alder Gulch in the early 1860s, thousands came to southwest Montana to mine gold and to profit from the miners. Originating in Corinne, Utah, the Montana-Utah Road crossed high plateaus and narrow canyons northward into southwestern Montana and became the best route for freighters supplying the mining camps. Wagons drawn by mule or ox teams carried loads of up to 12,000 pounds, the trip from Utah usually took three weeks, and a freighting outfit could often make three or four round trips a year. Near Dell, the road split into three trails leading to Bannack/Deer Lodge, Virginia City, and Helena, and this section ended at Helena. The arrival of the Utah & Northern Railroad in 1880 made the road obsolete, but it regained importance in the 1920s as U.S. Highway 91 and again in the early 1960s as Interstate 15.