Story highlights Emergency officials say it could be coming from Russia or Mexico

The only way to be sure is to conduct scientific testing on the substance

(CNN) A substance described as "white stuff" and "milky rain" is covering parts of Washington and Oregon states, but its origin is a mystery.

"We have received reports of 'white stuff' on vehicles. The ash is more than likely from the Volcano Shiveluch," Washington state's Walla Walla County Emergency officials said in statement.

The volcano, located on the Kamchatka peninsula in extreme northeast Russia, "spewed an ash plume to about the 20,000-foot level in late January," the agency says. "It has been deposited in a widespread area, including Washington and Oregon."

But in an updated post, emergency officials say it could be as a result of various reasons.

"While the substance is likely ash is from Volcano Shiveluch, they are a number of volcanoes that are currently active," they say. "The source of the material has not been scientifically confirmed."

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