Meriwether Lewis and William Clark were among the first to recognize this site as suitable for a trading post. Their expedition, from 1804 to 1806, passed through this area on its way to the Pacific Coast. They observed that the riverbank here had a gravel base and stood well above flood level, with cottonwood and ash readily available for construction. The site offered a broad vista that would keep approaching Indians from being concealed, while Indians on trading migrations could also see an outpost from a great distance. On the return leg of the journey, Lewis extensively surveyed and charted this site and the land near the junction of the Yellowstone and Missouri Rivers. Today, Fort Union is a designated stop on the Lewis and Clark National Trail.