YOSEMITE NATIONAL PARK -- A 26-year-old San Ramon woman plummeted 600 feet to her death Sunday while climbing the perilous summit cables on Yosemite National Park's Half Dome amid stormy, wet weather.

It was the 14th fatality this year in the sprawling wilderness full of towering cliffs and thundering waterfalls. Hayley LaFlamme, her sister and two friends had reached the top of the colossal escarpment and were just past the midpoint of the descent around noon when LaFlamme apparently slipped and lost her grip on the cables. She slid and tumbled down the nearly vertical granite slope to the rocks below. Search teams recovered her body later that day.

Park officials said a ranger at the base of the dome was checking the required hiking permits and warning visitors to avoid the treacherous climb, which is so steep in the last 400 feet that hikers must haul themselves up along thick metal cables to the summit.

LaFlamme and her companions were among about two dozen people who decided Sunday to brave the slick granite, which had been pounded by thunderstorms that morning. It wasn't clear Monday how many of the 20 or so other hikers on the world-famous outcropping, which rises 8,800 feet above sea level, witnessed the fall.

"The ranger told people that the weather was bad and not to go up the cables," said Kari Cobb, spokeswoman for Yosemite. "But ultimately it is the visitor's decision whether they want to take that risk."

Deadly year in park

It has been an especially deadly year at Yosemite, where fatal accidents are disturbingly common. In an average year, between five and six people die in the park between January and August, officials said.

Most of the accidents this year stem from the record Sierra Nevada snowpack, which has turned scenic summer rivers into raging whitewater. Last month, three Central Valley residents were swept over Vernal Fall. Their bodies have not yet been found in the rushing, rock-strewn Merced River. The trio ignored warning signs and scaled the safety railing atop the popular Mist Trail. They were standing in knee-high water when, one by one, they slipped and plunged 317 feet over the waterfall's edge.

LaFlamme and her companions also passed official warning signs. Near the base of Half Dome, a sign reads: "If a thunderstorm is anywhere on the horizon DO NOT PASS BEYOND THIS SIGN. Lightning has struck Half Dome every month of the year."

Rangers emphasize that Yosemite is a wild landscape, where visitors must be prepared for extreme weather conditions and hazardous terrain, not to mention the dangers posed by bears and other wildlife.

LaFlamme's death is still under investigation. It is not known whether she and her group were experienced hikers or had the proper equipment for the climb, Cobb said.

The National Park Service recommends that Half Dome hikers be in relatively good physical shape for the grueling 16-mile round trip, which covers nearly 5,000 feet in elevation change and takes about 10 to 12 hours to complete. Visitors should also have broken-in boots, gloves for the cable system and lots of water.

Still, hordes of visitors take a shot at Half Dome - and many of the park's other challenging trails - without doing their homework or wearing the necessary footwear. Flip-flops and sandals are common on the trail leading up to Half Dome, as are small children, the elderly and the overweight.

Perhaps most importantly, rangers warn climbers to keep an eye on the weather forecast. The National Park Service's Half Dome website states that climbers should scrap the ascent not only when storm clouds are visible but also when the ground is wet, since most accidents on the cables occur during rainy weather.

Previous fatalities

The last fatality on Half Dome occurred on June 13, 2009. Manoj Kumar, a 40-year-old software engineer from San Ramon, fell from the cables as rain, winds and hail buffeted the monument. Forty-one other hikers had to be helped down by rangers later that day.

Another hiker, Hirofumi Nohara, plunged from the cables on June 16, 2007. The other two deaths in recent years occurred when visitors attempted to ascend Half Dome when the supports were down and the cables were lying flat, as they are between mid-October and mid-May. Jennifer Bettles died on April 21, 2007, and Emily Sandal died on Nov. 8, 2006. Damp, slippery granite may also have been a factor in those deaths.

LaFlamme's death was the first since the park service instituted a permit system last summer that limits the number of Half Dome climbers to 400 each day. Prior to the permit policy, up to 1,200 people a day were squeezing onto the cables on peak weekends and holidays, creating dangerous logjams during the final scramble to the top.