LAS VEGAS, Nev. — Researchers at the University of Nevada-Las Vegas say they have discovered rocks with volcanic ash that could be as old as 12 million years.

UNLV researchers say the rocks were found due to the low water levels at Lake Mead. They also say the ash came from eruptions that occurred thousands of years ago in California, Idaho and Wyoming.

Additionally, researchers say in order to prepare for future volcanic eruptions in places like Yellowstone National Park the Long Valley Caldera in northern California that could send ash into Utah, it’s important to understand previous volcanic activity.

The last time these sedimentary rocks were visible was in the 1930s when the Hoover Dam was built. 

Researchers also say evidence was found of volcanic ash in other states in the western half of the United States.

Mark Jones contributed to this article.

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