Colter Peak, a 10,640-foot mountain in Yellowstone National Park’s southeastern Absaroka Range, became significant during the Washburn–Langford–Doane Expedition of 1870. On September 7, Lt. Gustavus Cheyney Doane and Nathaniel P. Langford made its first recorded ascent, gaining a broad view over Yellowstone Lake and the surrounding basin. From the summit, Langford sketched the first detailed map of Yellowstone Lake, while Doane recorded the complex volcanic landscape spread below. The mountain’s name shifted repeatedly: Henry D. Washburn first named it for Langford and Doane, Ferdinand V. Hayden reassigned those names, Philetus Norris later called it Mount Forum, and Arnold Hague gave it the official name Colter Peak.