A teenager who teaches wilderness survival fought off a bear after waking to find the animal biting his head and trying to drag him away.
The 19-year-old woke up at around 4am to a "crunching sound" with his head inside the mouth of the bear, which was trying to pull him out of his sleeping bag.
The teenager punched and hit it and other people who were sleeping nearby yelled and swatted at the bear, which eventually left.
The incident happened at Glacier View Ranch in Colorado, 48 miles north-west of Denver, a camp owned by the Rocky Mountain Conference of Seventh Day Adventists.
The teenager, identified only as Dylan, was treated briefly at hospital and released.
He told KMGH-TV that the bear dragged him 10 to 12 feet before he was able to free himself.
"The crunching noise, I guess, was the teeth scraping against the skull as it dug in," he said.
Dylan and some other staffers were near teepees where campers aged 12 and 13 were sleeping. None of them was hurt.
Black bears are not usually aggressive but have attacked several people in the US in recent weeks.
A woman and her dogs were attacked on Tuesday after they apparently surprised an adult bear and her cub in a huckleberry patch in the Idaho Panhandle National Forests.
Last month, black bears killed two people in Alaska in separate attacks.
Sixteen-year-old Patrick "Jack" Cooper of Anchorage was killed after he got lost and veered off a trail during a mountain race south of Anchorage.
Mine contract worker Erin Johnson of Anchorage died and her co-worker was injured in a mauling about 275 miles north-east of Anchorage.
Black bears will defend their young and have been known to paw and bite tents with food inside.
After the Colorado attack wildlife officers did not find any food that would have attracted the animal so they have set bear traps in the area and plan to continue a search for it with scent dogs on Monday.
The bear's behaviour was so atypical that any bear found in the traps in the next few days will probably be euthanised and officials will test later to see if it was the one involved in the attack using DNA evidence, Colorado Parks and Wildlife spokeswoman Jennifer Churchill said.