Mount Jefferson is a mountain in the U.S. state of Montana, and is one of the many 10,000+ ft peaks in the Tobacco Root Mountains. The mountain is located in Beaverhead-Deerlodge National Forest. (There is also another Mount Jefferson in Montana, further south, on the Idaho/Montana border.) Hollowtop Mountain is an adjacent, taller peak less than .75 miles (1.2 km) to the north. Over the years, the two summits have had numerous names and altitudes recorded on various maps. According to U.S.