GRAND JUNCTION, COLO. ? A climber who amputated his own arm with a pocketknife to free himself from a remote canyon in Utah had a strong will to survive, a rescuer said Friday.

Aron Ralston, 27, was hospitalized in serious condition Friday after his six-day ordeal in Blue John Canyon near Canyonlands National Park in southeastern Utah.

The experienced outdoorsman would have died if he had stayed in the canyon, pinned by an 800- to 1,000-pound boulder that had shifted onto his right arm, said Sheriff’s Department Sgt. Mitch Vetere.

“He said that was the only way out,” said Vetere, who helped rescue Ralston. “He had a will to live.”

In a statement, Donna Ralston said her son survived because of his strong physical and mental condition.

“He was able to rationally consider alternatives relative to his situation,” she said. “His spirits are high and he anxiously looks forward to returning to his love of the outdoors.”

Officials at St. Mary’s Hospital said Ralston was expected to recover.

Friends say Ralston’s expeditions have been known to inspire awe. He has climbed 49 of Colorado’s 14,000-foot peaks and was preparing for an ascent of Alaska’s Mount McKinley.

Aron Ralston is shown in an undated family photo. Ralston, 27, of Aspen, Colo., cut off his right arm below the elbow after he was pinned by a massive boulder. He was trapped for six days.

“To be honest, sometimes we get pretty scared with some of the things he’s doing,” said Brion After, manager of the Ute Mountaineering store in Aspen, where Ralston works.

Ralston began what was to be a day hike April 26. He was canyoneering, where a hiker uses rock-climbing gear to negotiate narrow canyons.

He pushed his arm into a crack in the canyon wall and the boulder shifted, pinning him, said Steve Swanke of Canyonlands National Park. He tried to use his ropes and anchors to free himself, but couldn’t.

On Tuesday, Ralston ran out of water. By Thursday, he decided he had no choice but to use his pocketknife to amputate his arm just below the right elbow, officials said.

He applied a tourniquet and administered first aid before rappelling 60 feet to the canyon floor, where he began walking.

He encountered two tourists and was about two miles from his car when a rescue helicopter spotted him, still bleeding, officials said.