I remain fascinated by this geologic phenomena. It is a world class example of a hillside saying “I’m in charge and will dump when I feel like it.” You can view it as you head to Yosemite towards the Arch Rock entrance. It’s kinda close to the park so it’s worth mentioning and keeping track of what’s going on.
In the spring of 2006, a 300-foot section of Hwy 140 north/east of Mariposa was covered by slate rocks. It was triggered by an exceptionally wet spring 2006, following a very wet spring 2005.
This photo shows how the event looked soon after the fall.
Total size of the fall was 800,000 cubic meters. It extended about a football field up the mountain. It has been stable ever since. CalTrans is now in the process of building a “Rock Tunnel” under it. As you cross the bridge you can look to the east and see the work.
The fear – worst-case, would be a rapid failure of the entire rock slide which would extend it across the Merced River, damming the river. This would create a reservoir. Bad news. As a temporary measure, traffic has been rerouted to the opposite side of the Merced River.
READ: How it will be fixed
A state-of-the-art monitoring system was installed to detect movement in the steep talus slope, movement of the main slide mass, local strong ground motion from regional earthquakes, and sudden changes in stream levels, possibly indicating damming of the river by slide material.
Unrelated thought worth quoting: “Duck and cover.” – 1950’s silly advice if we are hit by a nuke.
Read “One Best Hike: Yosemite’s Half Dome