03/18/2010 05:12 am ET Updated May 25, 2011

Aspen Trees Dying Off; Scientists Still Don't Have Definitive Reason

DENVER -- This should be the golden season across the West, when aspen paint hillsides in shades of fall.

But a mysterious ailment -- or perhaps a combination of factors -- is killing hundreds of thousands of acres of the trees from Nevada, New Mexico and Arizona through Utah, Colorado, Wyoming and into Canada, according to the U.S. government and independent scientists.

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