At least one person was killed and another injured after a rockfall on El Capitan, the most prominent granite cliff in Yosemite National Park, according to a statement from the National Parks Service.

The fatal rock slide, which was of “undetermined size,” according to a press release from the NPS, appears to have started near the Waterfall Route, a “popular climbing route” on the east buttress of the famous, nearly 3,000-foot granite wall.

“Park Rangers are working to transport the injured person to receive medical care outside of the park,” the statement reads. The rockfall comes during climbing season, and there are “many climbers” on the rock formation and other climbing routes in Yosemite.

The statement adds that the Yosemite remains open and visitor services unaffected.

Tour guide John DeGrazio was giving a tour of the park when he captured the moment of the rockfall.

“We saw a huge plume of smoke from the summit of Half Dome and later found out it was a fatal rockfall,” he told CNN.

“I am a guide on a tour right now. We were on the summit of Half Dome when we saw this.”

El Capitan is one of the world’s most famous climbs, known for its near-vertical cliffs. It was believed to be impossible to climb until 1957, when American rock climbing pioneer Warren Harding made it to the top with two aides.

In June, climber Alex Honnold became the first person to free-solo climb the mountain.