Yosemite Officials Issue Urgent Warning as Unusual Geological Phenomenon Could Risk Visitors’ Lives

Footage shared by Yosemite National Park, of August 26, 2009, displays a cluster of chalky white rocks detaching from a towering cliff, tumbling down, hitting a ledge, breaking into fragments, and plummeting into a giant talus heap. Today, dozens of cliffs and boulders in Yosemite Valley are carpeted with heaps like these, slathered with jumbled ballast, gravel, and broken stone. In fact, every boulder, every cliff, every rock structure of Yosemite is a story written by a series of “historic rockfalls” like these, the NPS writes. The ubiquitous rocks of Yosemite are both time capsules for explorers and warning signs for visitors to be mindful while they’re immersed in snapping selfies or hiking along a trail. The rock above their head or the boulder beneath their shoe could betray them at any time.

This is not to put the visitors on tenterhooks. This is just to train them in accordance with the intrinsic behavior of Yosemite’s rocks. With more than 4 million people visiting the park each year, ignorance of this crucial piece of information could be life-threatening. Rockfall, as the name suggests, is an incessant, uncontrollable skittering of loose rocks that detach from a cliff and start toppling downwards in an avalanche. NPS suggests that a rockfall can be triggered by a variety of geological processes, including glaciation, weathering, and bedrock fractures.

When the rocks platted with granite encounter powerful tectonic stressors and erosion forces, cracks start to materialize on their rugged surfaces. Over long periods, these cracks grow deeper and deeper, further weakened by the water flowing through them. And then all it takes is an intense gust of wind, an aggressive rainstorm. The cracks widen, the bonds break, and the cliff collapses into fragments.

Rockfalls aren’t new in Yosemite. Most of Yosemite has been sculpted and carved by a history punctuated with rockfalls. Historical records indicate that more than 1,000 rockfalls have dismantled, crumbled, and re-shaped Yosemite during the past 150 years. The Climbing Magazine recalls the famous rockfall episode that occurred in August 2023. The inch-wide crack, nicknamed “Super Natural,” emerged on the Royal Arches wall at the western side, north of The Ahwahnee Hotel.

Jesse McGahey, a Climbing Program Manager at Yosemite National Park, has a fond memory of the episode. After the crack appeared, a ranger was dispatched to the area, where they could hear it “cracking like a frozen lake that wasn’t consolidated.” McGahey describes, “And there were pieces of rock rattling down the crack without touching it.” The park geologist said they’d never seen anything like this.

2024 was relatively quiet with just 42 rockfalls. But on December 26, at 2:58 pm, the valley quivered. Approximately 98 tons of rock surrendered itself to the “Forbidden Wall” above the upper switchbacks. On April 15, 2025, visitors sleeping in the Pines campgrounds were shaken awake by uncanny thunderous sounds. Three days later, a ranger visited the closed section of the John Muir Trail and found that approximately 1,672 tons of rock had collapsed from just below the south rim of the canyon.

What should you do in the event of a rockfall? NPS offers three guidelines. To begin with, be aware of your surroundings. “If you witness a rockfall from the Valley floor, quickly move away from the cliff toward the center of the Valley. If you are near the base of a cliff, immediately seek shelter,” the park explains. Inform the park’s staff if you witness a rockfall, and lastly, understand the dynamic natural processes and act accordingly while exploring Yosemite Valley. The valley is smooth and the cliffs are dramatic, but no one can say what happens to the winds’ moods. If they turn hostile, the cliffs would have no choice but to surrender and disintegrate.