Yosemite Valley, located in California's Sierra Nevada mountains, is one of the most iconic landscapes in the United States. Known for its tall granite cliffs, beautiful waterfalls, and vast green meadows, the valley stretches almost eight miles and reaches a depth of 3,500 feet.
For decades, geologists have hypothesized that Yosemite Valley was shaped by a combination of natural forces, including tectonic uplift, water erosion, and glaciation. However, a new study suggests that there may be more to the story.
According to recent research, an ancient "ghost" river and an extinct volcano may have played a large role in carving Yosemite's dramatic U-shaped valley. Here's a closer look at the discovery and how it could reshape what scientists previously believed about the valley's formation.
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Scientists Believe Yosemite Valley Was Carved By An Ancient "Ghost" River And Volcano
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A new theory from Gabet may answer these questions. In a research article from April 2025, he suggests that between five and ten million years ago, before erosion from rivers and glaciers started carving Yosemite Valley, a chain of volcanoes once stretched across the northern Sierra Nevada. Mudflows from these volcanoes caused the landscape to slope.
Gabet explains that a river would have drained the volcanic chain and fed into what is now Tenaya Creek and the Merced River. He believes that the river, now long gone, was powerful enough to dramatically erode and shape the landscape into the current Yosemite Valley.
This "ghost" river could also explain the extreme depth of Tenaya Canyon, the volcanic debris in the Central Valley, and the inconsistent shape of the Tuolumne River valley. However, since both the river and the volcanoes have vanished, proving their existence remains a challenge.
"I realized these volcanic rocks that had been transported by the Merced River must have come from this chain of volcanoes," Gabet said.
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How Scientists Previously Believed Yosemite Valley Was Formed
The formation of Yosemite Valley, located in one of the most beautiful national parks in the United States, began between 105 and 85 million years ago when molten rock from a nearby volcano chain cooled and hardened into the granite under the Earth's surface. Over time, erosion stripped away the volcano and its surface layers, exposing the underlying granite formations.
Around 20 million years ago, the region slowly rose due to tectonic forces, helping to create the Sierra Nevada Mountain Range. As the slope became steeper, rivers began carving the granite into canyons and, eventually, valleys.
Lower Sardine Lake in the Sierra Butte region of the Sierra Nevada mountains
Then, between two and three million years ago, glaciers started to form in the Yosemite area. During this period, the Earth underwent over 40 cold and warm cycles. In the cold cycles, thick ice sheets flowed through the Sierra Nevada, dragging debris and rock with them. When they melted, they left behind the smooth granite rock faces that are still visible today.
Timeline of Yosemite Valley's Formation
220 million years ago:
The ancient landmass that would become North America began drifting toward its current location.
215 million years ago:
Subduction began, pushing the Farallon Plate (oceanic crust) below the North American Plate. Parts of the Farallon Plate melted. The molten rock either cooled underground or formed volcanoes.
105 to 85 million years ago:
Most of Yosemite's granitic rock formed underground.
85 to 15 million years ago:
Subduction ended, causing volcanoes and metamorphic rock to be eroded. The granitic rock was revealed.
20 to five million years ago:
Volcanoes formed and erupted again north of Yosemite.
Ten million years ago:
The Sierra Nevada region began to uplift, and rivers eroded the uplifted rock.
Two to three million years ago:
Glaciers formed, further carving out Yosemite Valley.
Despite the region's well-established geologic history, scientists still question why Yosemite Valley is so deep. While some say rapid tectonic uplift could have sped up the erosion process, many things remain unexplained.
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Questions Remained Unanswered Despite Yosemite Valley's Well-Established History
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One thing left unexplained about Yosemite's formation is Tenaya Canyon, a treacherous canyon known as the Bermuda Triangle of Yosemite that stretches from Tenaya Lake into the valley. Tenaya Creek currently flows through this canyon, but geologists believe it is much too small to have carved out such an impressive depth.
"It's just a really small river. You can jump across it. The mystery is, how did this tiny creek cut through thousands of feet of very resistant, very massive granite?" Manny Gabet, a geomorphologist at San Jose State University, told Live Science.
Geologists also found that the sediment accumulated in California's Central Valley from the Merced River includes a massive amount of volcanic material. The problem is that this volcanic material didn't exist anywhere near the river's current watershed, or source.
"You've got 8 cubic miles of volcanic sediment deposited in the Central Valley by the Merced River, but you can't find a scrap of these volcanic rocks," said Gabet.
Lastly, the Tuolumne River valley is noticeably deeper on one side than the other, an imbalance that has yet to be explained.
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Through this new study, scientists are realizing that Yosemite Valley's past is much more complex than once believed. If Gabet's hypothesis proves to be true, it could reshape how geologists understand not just Yosemite but many more iconic landscapes around the world.