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Mapped above are documented rockfalls in Yosemite Valley, from 1857 to 2020, for which location and seasonal timing are known.
What Is a Rockfall?
Rockfalls are a natural and dynamic geologic process involving the detachment and rapid downard movement of rock. Due to its steep, glacier-carved cliffs, Yosemite Valley experiences many rockfalls each year. Historical records indicate that more than 1,000 rockfalls have occurred in the park during the past 150 years. Massive piles of "talus" or rock debris at the base of Yosemite Valley's cliffs are reminders of these dramatic events. Natural processes like rockfall help to create the beautiful and changing scenery in Yosemite National Park, but they also present potential hazards.
A rockfall tumbles down the face of Half Dome on July 27, 2006.
Photo by Amanda Nolan
What Causes Rockfall?
A number of geologic processes set the stage for rockfalls, including glaciation, weathering, and bedrock fractures. Tectonic stresses and erosion cause granite rock to fracture. Rockfalls later occur along these fractures. Fractures that develop parallel to the surface are called sheeting joints. Sheeting joints create large slabs of rock that ultimately fall away in a process known as exfoliation. In Yosemite Valley, Royal Arches and the face of Half Dome are examples of landforms that have resulted from this process. Over long periods, water flowing through fractures decomposes the bedrock in a process called weathering. Weathering loosens bonds that hold rocks in place.
Triggering mechanisms like water, ice, earthquakes, and vegetation growth are among the final forces that cause unstable rocks to fall. If water enters fractures in the bedrock, it can build up pressure behind unstable rocks. Water also may seep into cracks in the rock and freeze, causing those cracks to grow. This process is called "frost wedging" or "freeze-thaw" and can incrementally lever loose rocks away from cliff faces. Recent research suggests that daily temperature variations and extreme heat can also cause rock slabs to become unstable. Ground shaking during earthquakes often triggers rockfalls. Additionally, a variety of vegetation-most notably firs, pines, and canyon live oaks-grow into the sheer rock faces where their roots expand and pry apart joints in the granite. Most rockfalls in Yosemite occur in the winter and early spring, during periods of intense rainfall, snow melt, and/or subfreezing temperatures, but many large rockfalls have also occurred during periods of warm, stable weather.
For any given rockfall, there is always a large degree of uncertainty about what exactly triggered it; historical records indicate that more than half of all documented rockfalls in Yosemite were not associated with a recognizable trigger.
Predicting actual rockfall events is not yet possible, but understanding the forces that trigger rockfalls is an important step toward this goal.
Computer modeling can help to identify potentially hazardous rockfall areas.
How Does Yosemite Address Rockfall?
The National Park Service in Yosemite is responding to rockfall in a variety of ways. Park scientists, in collaboration with the U.S. Geological Survey (USGS) and academic researchers, are actively studying rockfalls through the use of new technology, such as high resolution digital photography, laser mapping of cliffs, and exposure dating of boulders. These tools offer vast improvement in resolution from previously available data, allowing geologists to accurately map rockfall zones and to study rockfall source areas. Additionally, new computer modeling technology shows promise in simulating future rockfall behavior. The park is also actively investigating methods for monitoring rockfall activity.
The National Park Service has produced a report quantifying rockfall hazard and risk in Yosemite Valley to help improve safety and guide future park-planning efforts: Quantitative rock-fall hazard and risk assessment for Yosemite Valley, Yosemite National Park, California. Based on the results of this study, the National Park Service reduced rockfall-related risk in Yosemite Valley by removing or repurposing high-risk buildings within hazardous areas. These actions reduced rockfall-related risk by 95%.
Additionally, park rangers have developed emergency plans for rockfall events, and may close trails and post warning signs in particularly hazardous areas.
What Should I do in the Event of a Rockfall?
Be aware of your surroundings. Rockfall hazard zones occur throughout the park near any cliff faces. 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 or talus slope when a rockfall occurs above, immediately seek shelter behind the largest nearby boulder. After rocks have stopped falling, move quickly away from the cliff toward the center of the Valley. Be aware that rockfalls are inherently unpredictable and may happen at any time. Pay attention to warning signs, stay off of closed trails, and, if unsure, keep away from the cliffs.
Inform park staff if you witness a rockfall. If you witness or hear a rockfall of any size, please report it by calling 209/379-1420 or reporting it at one of the park Visitor Centers. This information is useful for assessing rockfall hazards and adds to the growing knowledge base of rockfall activity in the park.
Understand this dynamic natural process. Remember that Yosemite is a wild place. Rockfall is the most powerful geologic agent acting today in Yosemite. The dramatic cliffs of Yosemite are constantly being shaped by this potent natural force.
This rockfall from the "Porcelain Wall" (just west of Half Dome) on June 20, 2020, was 1,040 cubic meters in volume (nearly 3,100 tons).
Morgan Newport
Yosemite Rockfall Year in Review: 2025
2025 was a quiet year for rockfalls in Yosemite, with 43 documented events with a cumulative volume of approximately 478 cubic meters (1,423 tons). Both numbers, and particularly the cumulative volume, are below 20-year averages. As is typical, most of the documented rockfalls in 2025 consisted of relatively small rocks that fell onto park roadways during winter storms.
The two largest rockfalls in 2025 impacted park trails, though fortunately both occurred at night when there were no hikers. The first and largest rockfall occurred at 9:30 pm on March 31, when visitors in Curry Village heard a rumbling sound from the vicinity of Grizzly Peak. The first hikers on the Mist Trail the following morning encountered large boulders blocking the trail on the north side of the Vernal Fall footbridge. Approximately 150 cubic meters (446 tons) of rock had fallen from a point 385 m (1,270 feet) above the trail on the south side of Grizzly Peak, the same location as a similarly sized rockfall on February 5, 2024. That portion of trail was closed for several weeks as a trail crew blasted and cleared the boulders.
The second, smaller rockfall occurred at 1:25 am on May 8. Residents in Yosemite Village again heard rumbling in the night, and the following morning hikers on the Upper Yosemite Falls Trail encountered fresh rock debris on the traversing section of the trail between Columbia Point and the base of the Upper Falls. Approximately 80 cubic meters (238 tons) of rock had slid out from beneath an overhang, tumbling 55 m (180 feet) to the trail. The trail was briefly closed for assessment and initial debris clearing.
Other significant rockfalls in 2025 occurred from Glacier Point, Cathedral Rock, El Capitan, and the Snow Creek Trail.
If you witness a rockfall of any size or encounter fresh rock debris, please contact park geologist Greg Stock at 209/768-1028 or by email, or contact park dispatch by calling or texting 911 within the park. Documented rockfalls are added to the park database, enabling long-term evaluation of rockfall activity to improve public safety.
Get the details concerning the Ahwiyah Point rockfall on March 28, 2009, near Half Dome. This rockfall was the largest in Yosemite National Park since an even larger one occurred from Middle Brother in 1987.
"Evaluation of hypothesized water-system triggers for rock falls from Glacier Point, Yosemite National Park, California, USA" by Greg M. Stock et al, 2012, in Landslides and Engineered Slopes: Protecting Society through Improved Understanding, pages 1165-1171.
"Near-surface geophysical imaging of a talus deposit in Yosemite Valley, California" by Anna G. Brody et al., 2015, Environmental and Engineering Geoscience, v. 21, p. 111-127.
"Supporting evidence for a 9.6 +/- 1 ka rock fall originating from Glacier Point in Yosemite Valley, California" by Shaun E. Cordes et al, 2013, Environmental and Engineering Geoscience, v. 19, p. 345-361.
"Triggering mechanisms and depositional rates of postglacial slope-movement processes in the Yosemite Valley, California" by Gerald F. Wieczorek and Stefan Jager, 1996, Geomorphology, Volume 15, pages 17-31.
"Analysis of rock falls in the Yosemite Valley, California" by Gerald F. Wieczorek et al, 1995, in Rock Mechanics: Proceedings of the 35th U.S. Symposium, p. 85-89.
"Structural characterization of rockfall sources in Yosemite Valley from remote sensing data: toward more accurate susceptibility assessment" by Battista Matasci et al, 2011, Proceedings of the 2011 Pan-Am CGS Geotechnical Conference. [750 kb PDF]
Since the glaciers retreated around 15,000 years ago, rock fall has been the major force of change in Yosemite Valley. Geologists work to understand this force of nature in order to protect the millions of visitors who come here each year.
In this video, our roads and trails crew work to clear one of many rockslides that occurred in spring 2023 along the Big Oak Flat Road with drilling, blasting, and heavy equipment.
Footage taken after the 1996 rockfall at Happy Isles. On July 10, two blocks with a combined volume of about 30,000 cubic meters and weighing about 90,000 tons broke loose from near Glacier Point, hitting the valley floor near Happy Isles. The impacts generated an airblast with wind speeds up to 280 miles per hr. The wind uprooted and snapped about one thousand trees, which damaged buildings and caused one fatality and several serious injuries. A dense cloud of pulverized rock blanketed the area with dust.
