Sacajawea, the Shoshone woman who guided portions of the Lewis and Clark Expedition, led Captain Wm. Clark and his party of ten men over an old buffalo road through this pass on July 15, 1806. They were eastward bound and planned to explore the Yellowstone River to its mouth, where they were to rejoin Captain Lewis and party returning via the Missouri River. In the 1860s, John M. Bozeman, an adventurous young Georgian, opened a trail from Fort Laramie, Wyoming, to Virginia City, Montana, across the hostile Indian country east of here. He brought his first party through in 1863, and the next year guided a large wagon train of emigrants and gold-seekers over this pass while racing an outfit in charge of Jim Bridger, who used a pass north of here. These pioneer speed demons made as much as fifteen or twenty miles a day on some days, and the outfits reached Virginia City within a few hours of each other. In December 1883, the Northern Pacific Railway completed a 3,610 foot tunnel under the pass. By World War II, the old tunnel was badly deteriorated and could not handle the bigger railroad cars of the time. The railroad began boring a new wider tunnel under the pass in February 1944, completed it during the summer of 1945, and the new tunnel, still in use, is 3,015 feet in length.