On January 5th, a quiet and peaceful evening up Cedar Canyon was suddenly and violently halted.
Only a low gurgling noise from the nearly-frozen Coal Creek could be heard until several hundreds of tons of rock detached from the canyon's high rim and crashed across the hillside, pummeling trees and leaving large craters and gouges. Car-sized boulders twirled and bounced toward the river. The impact of the falling rock pulverized some of the material into a thick dust cloud that settled over this entire section of the canyon.
There were some pretty lucky people in the canyon that night. First, there was the snow-plow driver who drove through the canyon unscathed at 7:30. Then there were the motorists who slowed down when thick dust made the curvy road hard to follow, and were finally stopped when their headlights revealed the freshly-deposited mountain of rock blocking their path. After trying to make sense of the mess that laid before them, they turned around and called authorities from a nearby canyon restaurant at about 8:15.
A very small earthquake was recorded by the The University of Utah Seismograph Stations at 8:04. Seismologists at the U say the waveform of the event in consistent with an impact at the surface rather than a deeply sourced earthquake on a fault. You know you're dealing with a pretty serious rock fall when it is large enough to be recorded by seismographs.
Back to the people who first called it in at 8:15 - it is about a 10 minute drive from the rock fall to the restaurant, putting the motorists within a couple of minutes of being buried in this catastrophic event!
Above: looking up at the rock fall source area. The thick ledges of sandstone belong to the Tibbet Canyon Member of the Cretaceous Straight Cliffs Formation. This is normally a fairly competent unit, however, the Tropic Shale and Dakota Formation that form the slope below are extremely weak units that not only erode easily, but they are also prone to landslides. Both landslides and comparatively small rock falls have plagued this portion of the highway for years, but this is the first rock fall of this size. The crushed concrete barrier at the bottom of the photo was constructed to catch rock falls, but it certainly wasn't designed to stop anything this big.
Above: all 6 feet of me taking a closer look at one of the larger boulders that almost made it to the river.
After I climbed down along the boulders, I decided to cross the river and get a closer look from across the canyon. Looking back at my tracks, I noticed how much dust this thing produced and deposited on the opposite side of the canyon.
Above: the bulldozer here was no match for this moderate-sized boulder. UDOT anticipated having to blast several of the largest boulders, taking up to two weeks to clear and patch the road. They must have worked overtime, because they had the road open about 6 days later.
As part of the natural canyon-widening process, landslides and rock falls will continue to be an intermittent headache for UDOT in this part of the canyon. Lets just hope folks traveling through this canyon continue to have good luck.
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