Provocative study suggests super-deep Yosemite canyon may have been partially carved by ghost volcano and river

Scientists have proposed a new theory about the formation of Yosemite Valley. (Image credit: Yiming Chen/Getty Images)

A bold new hypothesis suggests that Yosemite Valley was formed by an ancient volcano and a vanished river that long ago ceased to exist.

Geologists have long debated why Yosemite Valley is so deep, with walls rising 4,000 feet (1,219 meters) above its base. The leading theory is that California's Sierra Nevada Mountains have undergone a period of uplift over the past 10 million years, making their slopes steeper and their rivers faster, eroding the granite around them.

But a new study published April 3 in the journal Geosphere argues that uplift is not the true cause of Yosemite’s formation. Instead, as study co-author Manny Gabet, a geomorphologist at San Jose State University, noted, the landscape of Yosemite and the surrounding Sierra Mountains is best explained by a long-vanished river.