SAN FRANCISCO - A friend who has scaled peaks with renowned rock climber Todd Skinner of Lander says he sometimes used gear beyond its life span, and fears a frayed climbing harness strap may have snapped, causing him to plunge to his death in Yosemite National Park.

It will take authorities days - possibly weeks - to officially determine why Skinner, 47, fell 500 feet to his death Monday while attempting to pioneer a new route up "Leaning Tower," an imposing rock face near Bridalveil Fall, the famous waterfall near the entrance to Yosemite Valley.

As Skinner lowered himself down the rock wall, a nylon loop attaching his harness to the rope broke, and he fell, hitting the side of the mountain, said his close friend Paul Piana, who received an emotional call from Skinner's climbing partner, Jim Hewitt, on Monday afternoon.

"Jim told me it was some equipment that was too worn, which makes it really tragic," Piana said. "Todd and I have contributed to the design and tested a lot of equipment, so we have a lot of faith in its durability. Sometimes maybe because of that, you become a little too complacent."

Iconic among outdoor adventurers as the birthplace of modern rock climbing in North America, Yosemite's mammoth rock faces and craggy granite formations have a particular allure for climbers eager to push the boundaries of the extreme sport. In 1988, Skinner and Piana became the first to climb El Capitan, the park's massive 3,000-foot monolith, using a technique called free climbing, in which climbers ascend using no artificial aid to climb - just a rope to protect against falls.

Rock climbers represent a very small proportion of injuries and fatalities in Yosemite, said Adrienne Freeman, a park spokeswoman. And despite public perceptions of the sport's dangers, statistics show fatal accidents are rare.

The Golden, Colo.-based American Alpine Club estimates there are about 250,000 climbers in the United States and Canada. In a typical year, there are between 10 and 40 fatalities attributed to rock climbing and mountaineering, said Phil Powers, the club's executive director.

"Because of the danger and the advanced skill necessary both to move over the terrain and manage the safety systems that one needs to protect oneself, climbers are very much living in the moment," Powers said. "In some respects, it's sort of like the yoga of the mountaineering world."

Skinner, who grew up near Pinedale, was celebrated for blazing new paths up hundreds of sheer faces from Canada's Yukon Territory to the Himalayas by following the natural lines of weakness - tiny cracks, wedges and edges - in the rock.

His physical control even in the most precarious of positions won Skinner the respect of his peers and helped inspire a new generation of climbers, said Daniel Duane, author of "El Capitan: Historic Feats and Radical Routes," a history of big wall rock climbing in Yosemite.

"Each generation of climbers has kind of a shining light, and Todd has been that shining light for several generations," said Piana. "I never thought he would go climbing, not in this way."

Freeman said it was too early in the investigation for park officials to speculate why Skinner fell.

"You're not necessarily talking about climber error or equipment failure," she said. "You have a whole range of things that could go wrong."

For that reason, those new to the sport may prefer sport climbing in gyms or on artificial walls, relatively risk-free endeavors.

"Whenever you possibly can, you don't put all your life on one piece of gear, but sometimes it's impossible," said Yvon Chouinard, an avid climber and owner of Patagonia Inc., an upscale outdoor gear-maker and clothier. "People have been doing the exact same thing Todd was doing for a long time, and the fact that the strap would break is pretty shocking."