One person was killed and another injured after a large rock broke off Yosemite National Park’s popular El Capitan rock formation Wednesday, officials said.

The rock fell from one of the world’s most famously scaled granite monoliths about 1:55 p.m. Wednesday. The rock was released near the “Waterfall Route,” a popular climbing route on the East Buttress of 3,000-foot-tall El Capitan, said Danielle Bonnici, a park ranger and Yosemite spokeswoman. The size of the rock fall has not yet been determined, she said.

Craziest thing ever witnessed a rock slide on El Capitan. Video not great I had to dig out my phone

Posted by Karen Brothers on Wednesday, September 27, 2017

She said officials could not provide an update on the status of the injured person, who was transported to a hospital from the park, which is about 150 miles east of San Francisco. Officials are using a helicopter to search the area for any other people injured in the rock fall, which occurred on a day with clear blue skies at the height of climbing season.

Multiple 911 calls reporting the rock fall were made just before 2 p.m., she said. Park officials are investigating why the rock fell.

Yosemite National Park El Capitan rockslide.

A post shared by YExplore Yosemite Adventures (@yexplore) on

John P. DeGrazio, a wilderness guide in Yosemite, said the hiking group he was leading had stopped to take pictures on the summit of Half Dome, another famous monolith in Yosemite, when they saw a “huge plume of smoke” come from El Capitan.

“At first, we thought it could have been a fire,” he said. “Once we saw how quickly it dissipated, we knew it wasn’t a fire. When someone said it was a rock fall, I immediately thought of the climbers and knew it could be potentially bad.”

On the way down, a park ranger told DeGrazio there had been a death.

Among the hiking group, he said, there was “definite surprise and obvious remorse” for the victims and their families. The hikers were also concerned for their own safety.

“They’re thinking, ‘We’re on big rocks, too,’ ” he said. “There is always risk.”

An ABC30 reporter said a Yosemite climber sent her a photograph of the rock fall, during which he said “a piece of granite the size of an apartment building came crashing down the Waterfall Route.”

El Capitan is considered the “Mount Everest of rock climbing,” with thousands ascending it each year.

There were 58 rock falls in Yosemite in 2016, which was slightly lower than in previous years, according to the National Park Service.

Sometimes, rock falls have obvious causes, including storms or earthquakes, while others occur on clear, sunny days.

“We have a lot of rockfalls in Yosemite because the cliffs are so big and steep,” Greg Stock, Yosemite’s park geologist, told the Smithsonian Magazine.

The rocks break away in giant slabs because they are destabilized by small contractions that come with changes in season and temperature. Usually, the trigger is something recognizable, but the heat of the day can also be enough to cause a slab to fall, he said.

Stock said that in the past 150 years, about 15 people have died as a result of rock falls.

He has tried to reduce the hazard of rock falls by moving buildings and places where hikers congregate away from cliffs from which rocks might tumble, according to the Smithsonian.

Read more:

A Southwest passenger complained about dogs on her flight. Police forced her off the plane.