GROVELAND, Calif. (AP) -- As firefighters make progress containing a raging wildfire in and near Yosemite National Park, officials have turned to unmanned aircraft to monitor for unexpected developments.
The California National Guard launched a drone Wednesday in an effort to get an early bead on spot blazes.
Incident commander Mike Wilkins said Wednesday that the unmanned MQ-1 aircraft already is giving ground-based crews a birds-eye view of new developments.
"Already this morning it's allowed us to see a spot fire we wouldn't have seen," he said.
A similar unmanned NASA aircraft has been used for fire surveys in past years.
The drone took off from the Victorville Airport in Southern California and generally flew over unpopulated areas on its 300-mile flight. While outside of the fire area it will be escorted by a manned aircraft.
Officials were careful to point out images are being used only to aid in the effort to contain the Rim Fire burning in the western Sierra Nevada.
Wilkins said they'll use the information the drone broadcasts to decide in real time where to deploy resources. They also hope to use it to detect any changes on the ground that could threaten crews.
In 2009 an unmanned NASA Predator equipped with an infrared imaging sensor was used to help the U.S. Forest Service assess damage from a fire in Angeles National Forest. In 2008 a drone capable of detecting hot spots helped firefighters assess movement of a series of wildfires stretching from Southern California's Lake Arrowhead to San Diego.
The Rim Fire has burned through 293 square miles of the Sierra Nevada, destroyed 111 structures and threatened giant sequoias.
Fire officials say they expect full containment in three weeks but that it 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 has threatened San Francisco's water supply at the Hetch Hetchy Reservoir, the only municipal water supply inside a national park. Stratton said Wednesday that the fire is burning itself out as it approaches the reservoir and that crews are lighting back burns on the south side of the reservoir to push it back into the wilderness area.
Pushed by winds blowing to the north and east, the largest fire in Sierra Nevada recorded history has unleashed a smoky haze that has worsened air quality more than 100 miles away in Nevada.
Most of the structures that were destroyed are tent cabins and other outbuildings, but 11 homes have been lost, said California fire spokesman Daniel Berlant.
On Wednesday morning, authorities said the blaze was 23 percent contained, with crews aided by higher humidity continuing to make progress against it overnight.
"Our crews are getting the upper hand on this fire," Berlant said.
The fire started Aug. 17 and investigators are trying to determine the cause.
Associated Press reporter Scott Sonner contributed from Reno, Nev.