Associated Press
In this May 11, 2012 photo, Jeffrey and Ponderosa pines show telltale signs of yellowing, a symptom of ozone toxicity, in Sequoia National Park, Calif. A big city problem has settled in a big way in Sequoia Kings Canyon National Park, home of the giant Sequoias. Smog from the neighboring Central Valley is making it tougher for seedlings from the giants to take hold, and the needles of surrounding Jeffrey and Ponderosa pines are yellowing. (AP Photo/Tracie Cone)

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