The climbers were asleep in their tents, hoping to get a few hours rest before a pre-dawn ascent of Africa's highest peak, when the boulders rained down. Three Americans were killed and two others seriously injured.

The Americans were among several dozen foreign climbers from various tour groups camped near Arrow glacier on Kilimanjaro's difficult Western Breach when the rock slide occurred Wednesday.

The dead were identified as Kristian Ferguson, 27, of Longmont, Colo.; Mary Lou Sammis, 58, of Huntington, N.Y., and Betty Orrik Sapp, 63, of Melrose, Mass.

The climbing trip was a lifelong dream of Sapp and her husband, William W. Sapp Jr., both physicists, said neighbor Jeannine Holden. The husband survived.

"They were so thrilled. They were looking forward to bringing us back pictures," Holden said.

Ferguson, a satellite engineer at Ball Aerospace & Technologies Corp. in Boulder, Colo., had been hiking with his wife and others from the Colorado Mountain Club, friends and club officials said.

"Kris had a lucky star, up until the day before yesterday," said his father, Paul Ferguson, of Redmond, Wash. "He was always energetic and brilliant at whatever he tried. He was able to deal with the most technical problems and yet he was the most cerebral type of person when it came to things like psychology and philosophy and poetry."

"He was charmed and charming," said his mother, Karrie.

Ferguson said Jodi Coochise, his daughter-in-law, told him the couple was in their tents when the rock slide occurred.

Debbie Ramsey, a family friend answering the telephone at the Sammis home, said Sammis was in Tanzania with her husband, Scott, and three adult children.

"It was a dream come true for them," Ramsey said of the family's trip.

Mary Sammis "loved to hike and was always going on hiking trips with friends," Ramsey said. "Mary was a very upbeat, wonderful, great friend."

The injured Americans were flown to Nairobi, Kenya, for treatment, said James Wakibara, acting spokesman for Mount Kilimanjaro National Park.

Several Tanzanian guides also were initially reported killed, but regional police commander Mohamed Chico said Thursday that no Tanzanians had been found among the dead.

Of the world's top peaks, Kilimanjaro is among the easiest to scale — though, as Wednesday's slide demonstrated, it can be deadly.

The climbers set out Saturday to climb the Umbwe route, the most difficult on Mount Kilimanjaro, which at 19,443 feet is the highest freestanding mountain in the world. Even so, the route is only a very difficult hike, not requiring safety ropes or special equipment.

The group had taken several days to reach the camp at Arrow glacier, the normal resting point at 15,800 feet, before summiting Uhuru peak along the Umbwe route. Climbers usually arrive before nightfall and sleep until they begin the ascent at around 2 a.m. to reach the summit at dawn.

Above the camp site is a steep slope of loose gravel and above that is the crater wall of a now extinct volcano. While the climbers were sleeping, boulders and rocks broke off the wall and fell on the camp site, said Thomas Kimaro, owner of Alpine Tours.

Wakibara said a rescue team was immediately sent up the mountain along with every available porter to help bring down the dead and injured. By Thursday morning, more than 50 foreign climbers had been brought down, some with minor injuries, and the Umbwe route was clear, he said.

More than 20,000 tourists attempt to climb the mountain every year. About 10 people die each year during the climb, usually from high altitude sickness.

But rock slides are rare, Wakibara said.

"The possible explanation I hear on this could be earth movement or vibration," he said. "It has never happened like this in the past."

Chico said experts were on the mountain Thursday trying to determine what caused the slide. There had been a change in the weather at the peak before the rock fall, officials said, without elaborating on how that could have contributed to the accident.

Warmer temperatures over the last decade have melted some of Mount Kilimanjaro's glaciers, causing them to retreat, which has loosened rocks once held in place by the ice.

Climbers on other routes were allowed to continue on Thursday, Wakibara said.