 After months of unemployment in the frontier territory, Everts took the opportunity to accompany an expedition led by Henry D. Washburn and Nathaniel P. Langford into the still largely unexplored wilderness that would later become Yellowstone National Park.The Washburn–Langford–Doane Expedition of 1870 was the second official survey of the Yellowstone region in less than two years.After falling behind the rest of the expedition on September 9, 1870, Everts managed to lose the pack horse which was carrying most of his supplies.