Organized as one of the original Colorado counties, Summit has a total area of 619 square miles (1,600 km2) and about 80% is public land. Terrain is mountainous with elevations ranging from 7,957 feet (2,425 m) at Green Mountain Reservoir to 14,270 feet (4,350 m) at Grays Peak. Come find out why people live longer here than in any other county in the United States. Explore  Summit.