Two experienced climbers fell to their death Saturday morning as they ascended a challenging route on Yosemite s El Capitan.

Officials reported receiving several 911 calls after the tragic accident on the Freeblast Route of the 3,000-foot granite monolith in the California national park. Rangers responded immediately, but said by the time they arrived the climbers had already died.

The circumstances around the fall are under investigation, and we are working to understand what happened, Park Ranger Jamie Richards said.

The climbers were identified as Jason Wells, 46, of Boulder, Colo., and Tim Klein, 42, from Palmdale, Calif. They were attempting to ascend the Freeblast Route on the southwest side of El Capitan.

The deaths occurred almost two weeks after a fatal accident May 21 when a hiker lost his grip in rainy weather on cables installed for climbs at Yosemites Half Dome.

Last fall, a climber was killed in a rockfall on El Capitan . Renowned rock climber Dean Potter, 43, died along with his partner BASE jumping off Taft Point in Yosemite in 2015.

Just last week, two climbers set a speed record ascending The Nose route of El Capitan. Alex Honnold and climbing partner Tommy Caldwell on Wednesday raced up the nearly 90-degree face in 2 hours, 10 minutes and 15 seconds.