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Stanford Research: Northern Sierra Nevada Formed Nearly 40 Million Years Ago

STANFORD (CBS SF) – Scientists at Stanford University have published new research suggesting the northern part of the Sierra Nevada mountain range was formed tens of millions of years ago, far earlier than previously thought.

Researchers determined the northern Sierra Nevada reached its current height about 40 million years ago, during the Eocene period. They also found the climate of the Northern Sierra was significantly warmer than the mountain range today.

Study lead author Hari Mix, who is now an assistant professor at Santa Clara University, told CBS San Francisco that researchers analyzed ancient river rocks from Gold Rush-era mines in the Motherlode. They separated out clays from the rock and analyzed the oxygen isotopes.

Google Map Shows Northern Section of Sierra Nevada Mountain Range
(Google Map)

The research echoes a Stanford study published in the Journal Science in 2006 that also suggested the mountain range reached its current elevation about 40 million years ago. In that study, the researchers analyzed hydrogen in the same samples to determine age and elevation.

"The preponderance of evidence that the Northern (Sierra) were high since 40 million years ago is just crushingly definitive," study co-author and Stanford professor Page Chamberlain said in a university statement.

For decades, scientists believed the Sierra Nevada was considerably younger, formed between 3 million to 5 million years ago. According to Mix, the range started as a chain of volcanoes 100 million to 60 million years ago.

Mix is conducting research to determine the age of the Sierra Nevada in Yosemite and in the southern part of the range.

The study has been published in the Geological Society of America Bulletin.

Tim Fang is a digital producer for CBS San Francisco. A native of the Bay Area, follow him on Twitter @fangtj.

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