After a full day on the mountain Thursday, authorities ended rescue efforts in their search for a snowmobiler caught in an avalanche Wednesday in the La Plata Mountains near Sharkstooth Peak. He is presumed to have died.

"We're officially calling it a recovery now," Montezuma County Undersheriff Lynda Carter said Thursday night. "If there was a chance he was still alive, we'd be moving heaven and Earth, but it's just too dangerous to go up there for a recovery."

Carter said snow is forecast in the slide area for the next few days, which factored into the decision.

"It may only snow an inch in town," she said, "but it will be 3 feet up there. We consulted several experts, including from the (Colorado Avalanche Information Center), and they said no way we should go up there without blasting. Even the trail up the mountain isn't safe."

The missing snowmobiler has been identified as Montezuma County resident Robert "Rob" Yates. His companions - Chris Sharp, Bryce Rogers, Rodney Rule and Rod Oliver - all escaped with minor cuts and scrapes after digging themselves out. Rod Oliver is the father of Seager Oliver, state wrestling champ from Montezuma-Cortez High School.

They were all experienced snowmobilers familiar with the area, Carter said.

Rescuers described the search scene as remote backcountry, about 20 miles into the La Platas, with unstable snowpack. The avalanche was large, spanning 100 yards wide and three-quarters of a mile long. It let loose in a steep chute while Yates was attempting to free a stuck snowmobile, rescue officials said.

The slide occurred at 10,500 feet on the northeast side of Sharkstooth in the Bear Creek drainage. An emergency call was made to the Mancos Fire District Wednesday about 1 p.m. Three snowmobilers stayed at the accident scene while one person rode up to a ridge to call for help.

Yates' snowmobile was found with a probe 8 feet under the snow Wednesday, but the debris flow was estimated to be 30 feet deep.

"We did manage to dig out the snowmobile today to see if he was in a pocket," Carter said, "but we didn't find anything other than the sled and helmet we found Wednesday."

Brian Lazar, deputy director for the avalanche information center, reported that the accident is a confirmed burial, based on eyewitness accounts.

Montezuma County Sheriff Dennis Spruell said 10 rescuers, three snowmobiles and two helicopters searched the area until dark Wednesday. The search resumed Thursday morning with 22 snowmobiles and almost 30 people, Carter said, and included expert avalanche investigators and searchers, search dogs and helicopters.

"The Blackhawk helicopter from Buckley Air Force Base allowed us to search a much larger area," she said. "They ferried people from the bottom of the chute to the top in seconds, rather than making them climb for an hour in deep snow to get up."

The snowmobilers did have avalanche beacons, but even a rescue helicopter monitoring the scene from the air could not detect a signal.

Avalanche conditions are considered high right now in the backcountry, said Kirk Underwood of United Search and Rescue.

"The snowpack is very unstable, with a lot of layers and heavy snow," he said. "My advice would be to stay away."

Carter was heartened by the number of people who turned out both to search and to support the family, with 25 to 30 people at the command center all day.

"That shows how highly he was thought of," she said. "So many people took the day off to come help with the search."

Ann Butler of the Durango Herald and Jim Mimiaga of The Cortez Journal.