Roadside turnout, gravel, with historical information sign. 'Fort Union - Fort Union, one of the largest and best known trading posts of the fur days, was located on the Missouri River near the mouth of the Yellowstone, about 14 miles southeast of here. Built by the American Fur Co. in 1828 for trade with the Assinniboine Indians, its importance increased with the arrival of the first steamboat from St. Louis, the 'Yellowstone.' about June 17, 1832.' City of Glasgow to Montana/North Dakota State Line Welcome to Montana! From the wondrous geological features of Yellowstone to the majesty of Glacier, Montana\'s National Parks inspire and astound. The famous Lewis and Clark Expedition crossed Montana in 1805 and then again in 1806. Montana offers Rafting, hiking, hot springing, fly fishing, horseback riding, rock climbing, mountain biking, skiing hunting and more.