The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Firefighters gained some ground Tuesday against the huge wildfire burning forest lands in the western Sierra Nevada, including parts of Yosemite National Park. (AP Photo/Jae C. Hong)
The giant wildfire burning at the edge of Yosemite National Park is 30 percent contained, U.S. fire officials said Wednesday
The U.S. Forest Service said the fire has now consumed 301 square miles (780 sq. kilometers).
Fire officials said they expect full containment in three weeks but that the fire will burn for much longer than that.
"It's looking better every day," said incident spokesman Glen Stratton. "So far everything is holding."
The fire in northern California has destroyed 111 structures and threatened water supplies, hydroelectric power and giant sequoia trees—a state icon. Some 4,500 structures remained threatened.
Stratton said the fire was burning itself out as it approached the reservoir that supplies the city of San Francisco with water.
The fire, one of the largest in state history, also has caused air pollution problems in California cities far from the scene.
Forestry experts said unnaturally long intervals between wildfires and years of drought primed the Sierra Nevada mountains for the explosive fire in the rugged landscape.
Federal forest ecologists said historic policies of fire suppression to protect timber interests left a century's worth of fuel in the fire's path.
Firefighters enter a grove of giant sequoias in Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the National Park Service on Tuesday. Yosemite crews continue to protect the Merced and Tuolumne groves of giant sequoias less than 10 miles from the front lines of the Rim Fire, which has ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history. (AP Photo/National Park Service)
Two years of drought and a constant slow warming across the Sierra Nevada also worked to turn the Rim Fire into an inferno.
For years, forest ecologists have warned that Western wildfires will only get worse.
A fire crew digs a fire line near Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the US Forest Service on Tuesday. Firefighters continue to battle the Rim Fire, which has ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history. (AP Photo/US Forest Service, Mike McMillan)
The California National Guard launched an unmanned aerial drone Wednesday in an effort to get an early look at fires. A similar unmanned NASA aircraft has been used for fire surveys in past years.
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