Eldorado Mountain, Mountain summit in Boulder County, Colorado, US

Eldorado Mountain is an 8,344-foot (2,543 m) summit on the eastern flank of the Front Range, 8.1 miles south by west of downtown Boulder, Colorado. It straddles the Boulder County–Jefferson County line, rises about 2,500 feet (760 m) above its northeast toe, and measures roughly two miles across on a southeast axis. Near the top, a large antenna field with two buildings overlooks the steep east slope; radio station KBCO transmits from the site.

The Crags Hotel opened near the top of the Rattlesnake Gulch Trail in 1908 and burned down in 1913. It ran a funicular down to South Boulder Creek. Eldorado Canyon State Park has turned the hotel ruins into a historic site for visitors. The trail climbs about halfway up the mountain's north flank.

The name was probably borrowed from the nearby community of Eldorado Springs, at the mountain's northern foot. On the north flank, the Rattlesnake Gulch Trail climbs about halfway up to the ruins of the Crags Hotel, which the state park has turned into a historic site; the hotel ran a funicular down to South Boulder Creek. Down the access road from the old Conda Quarry stands the Eldorado Mountain Yoga Ashram.

The summit is owned by the City of Boulder, which restricts public access to this part of its holdings, and no trail leads to the top. The only trail on the east side is a climber's path to Mickey Mouse Wall. The Rattlesnake Gulch Trail in Eldorado Canyon State Park climbs about halfway up the north flank to the Crags Hotel ruins.

Mickey Mouse Wall, the mountain's largest cliff, sits on the east flank. Seen from the north, two buttresses at its top form a pair of mouse ears; from the east it reads as one of the Flatirons. The only trail on this side is a climber's access path, which the City of Boulder planned to realign as of September 2007.