How Old Is Yosemite Valley?

Above, an early morning view of Yosemite Valley. Photo by Armand Vaquer.

It was while I was in fourth grade that I first learned about Yosemite National Park in California. It was there that I learned about Yosemite Valley and the prominent mountain formations such as El Capitan, The Three Brothers and Half Dome.

Scientists have been studying the formation of Yosemite Valley and have new estimates on its age and how it was formed.

An article in the Lake County News begins with:

BERKELEY, Calif. — First-time visitors to Yosemite Valley gape in awe at the sheer granite wall of El Capitan and the neatly sliced face of Half Dome, aware, perhaps vaguely, that rain and glaciers must have taken a long time to cut and sculpt that landscape. But how long?

Did it all start 50 million years ago, when the granite through which the valley cuts was first exposed to the elements? Was it 30 million years ago, when data suggest canyons in the southern Sierra Nevada began to form? Did the valley only begin to form after the Sierra tilted toward the west some 5 million years ago, or was it mostly due to glaciers that formed in a cooling climate 2 to 3 million years ago?

Geologists from the University of California, Berkeley, employed a novel technique of rock analysis to get a more precise answer, and concluded that much of Yosemite Valley’s impressive depth was carved since 10 million years ago, and most likely even more recently — over the past 5 million years. This shaves about 40 million years off the oldest estimates.

Rivers performed the initial carving in a preexisting shallow valley, they determined, and then both rivers and ice contributed recently.

While the scientists are unable to be more precise, the new estimate is the first to be based on an experimental study of the granite rocks in and near Yosemite, rather than on inferences based on what was going on elsewhere in the Sierra Nevada.

To read more, go here.