Mount Massive is the second-highest summit of the Rocky Mountains of North America and the U.S. state of Colorado. It is located in the Mount Massive Wilderness of San Isabel National Forest, 10.6 miles west-southwest of the City of Leadville in Lake County, Colorado, United States. Mount Massive edges out the third-highest summit of the Rockies, M…Mount Massive is the second-highest summit of the Rocky Mountains of North America and the U.S. state of Colorado. It is located in the Mount Massive Wilderness of San Isabel National Forest, 10.6 miles west-southwest of the City of Leadville in Lake County, Colorado, United States. Mount Massive edges out the third-highest summit of the Rockies, Mount Harvard, by 2 feet, but falls short of Mount Elbert by 14 feet. It ranks as the third-highest peak in the contiguous United States after Mount Whitney and Mount Elbert.