The two were apparently snowboarding above Yankee Doodle Lake, a couple of miles southwest of Eldora's boundaries. The area, at about 10,700 feet, is popular for backcountry skiers and snowboarders and is accessible from the resort, McGrath said.
The avalanche happened about 1 p.m., McGrath said. It was about 900 feet wide and 500 feet long and swept Vaughn into the lake, said Dave Booton of the sheriff's office.
Both snowboarders were wearing avalanche beacons and appeared to have triggered the slide, said Kent Sperry of the sheriff's office. Searchers did not receive a signal from the missing snowboarder's beacon, officials said.
It was the first avalanche accident of the season, authorities said.
There have been numerous avalanches across the state since Thanksgiving, according to the Avalanche Information Center, but this was the first one reported involving people.
Last year, four people died in Colorado in avalanches. At least five others were caught in avalanches but escaped with minor injuries, according to the information center.