Yosemite Valley’s origin story has been a subject of debate for decades. Now, geologists from the University of California, Berkeley, have used a new rock analysis technique to find the true age of Yosemite Valley.
The study showed that most of Yosemite Valley’s depth was cut within the last 10 million years, reducing the oldest estimates by about 40 million years. The team found that a shallow valley was initially cut by rivers, with both ice and flowing water contributing more recently.
While the scientists are unable to be more precise, the new estimate is the first based on an experimental study of the granite rocks in and near Yosemite, rather than studies based on other areas in the Sierra Nevada.
“The question really is whether the elevation has just been coming down through erosion since that time or whether it came down some and then was uplifted again more recently,” said Yosemite National Park geologist Greg Stock. “At this point, based on studies I’ve done for most of my career and supported by this study, I see a lot of evidence for recent uplift happening sometime in the last 5 million years.”
That uplift, which happened at the same time that earthquake faulting in the eastern Sierra Nevada created an escarpment several kilometers high, steepened the western slopes and rivers, causing them to incise valleys more quickly.
“The brief history of Yosemite Valley would be that there was some kind of valley in place for tens of millions of years — a river-carved canyon associated with the ancient Sierra Nevada,” said Stock. “And then, in the last 5 million years or so, renewed uplift of the range through westward tilting caused rivers to steepen and deepen the canyons that they were in.”
That uplift likely carved out more of Yosemite Valley and may have started forming Tenaya Canyon within the past 5 million years. In the last 2 to 3 million years, as the climate cooled and glaciers came down through Tenaya Canyon and into Yosemite Valley, they further sculpted the rock, deepening those valleys and widening them considerably.
The new study provided significant insight into the geographic history of Yosemite National Park, known for its iconic rock formations, valleys and waterfalls.
“The timing of this new study is perfect in the sense that, over the next several years, we’re hoping to completely redo the Geology Hut displays at Glacier Point.” said Stock. “I’m very excited to include these new results in those displays.”