1. Various of flames burning outside Yosemite National Park
2. Tracking shot of burned trees
3. SOUNDBITE: (English) Lee Bentley, US Forest Service fire fighter:
"It went through real quick. You can see how intense it is. As we drove here today you can see all the black, how intense this fire has been."
4. Fire engine arriving
5. Burned forest
6. Various of burned structures around a lake
7. Various of firefighters extinguishing burning debris
8. SOUNDBITE: (English) Lee Bentley, US Forest Service fire fighter:
"We're starting to get a little bit of a handle on this thing. It's been a real tiger. He's been going around trying to bite its own tail and it won't let go but we'll get there."
9. Various of burned vehicle
10. Charred houses
ABC - NO ACCESS NORTH AMERICA
Tuolumne County, California - August 26, 2013
11. SOUNDBITE: (English) Edmund G. Brown Jr., California Governor:
"Well the water concern is that as the months go on and the winter comes and the floods move all the ash and loose debris onto the water and the water gets contaminated, that's bad. So whatever the firefighters can do to prevent that, we're doing."
A raging wildfire in Yosemite National Park rained ash on the reservoir that is the chief source of San Francisco's famously pure drinking water, and utility officials on Monday scrambled to send more water toward the metropolitan area before it becomes tainted.
Nearly 3,700 firefighters battled the approximately 230-square-mile (600-sq. kilometre) blaze, the biggest wildfire on record in California's Sierra Nevada.
They reported modest progress, saying the fire was 15 percent contained.
The Rim Fire has threatened two groves of giant sequoias that are unique in the region, prompting park employees to clear brush and setting sprinklers.
Utility officials monitored the Hetch Hetchy Reservoir for clarity and used a massive new 4.6 (b) billion US dollars gravity-operated pipeline system to move water quickly to reservoirs closer to San Francisco.
The Hetch Hetchy supplies water to 2.6 (m) million people in the Bay area, 150 miles (240 kilometres) away.
Officials are concerned that runoff during spring flooding will dump ash and charred debris into the reservoir, contaminating it.
"So whatever the firefighters can do to prevent that, we're doing," said the California governor.
So far the ash that has been raining onto the Hetch Hetchy has not sunk as far as the intake valves, which are about halfway down the 300-foot (90-meter) O'Shaughnessy Dam.
Utility officials said that the ash is non-toxic but that the city will begin filtering water for customers if problems are detected.
That could cost more.
On Monday the fire was still several miles away from the steep granite canyon where the reservoir is nestled, but several spot fires were burning closer, and firefighters were protecting hydroelectric transmission lines and other utility facilities.
Power generation at the reservoir was shut down last week so that firefighters would not be imperiled by live wires.
San Francisco is buying replacement power from other sources to run City Hall and other municipal buildings.
It has been at least 17 years since fire ravaged the northernmost stretch of Yosemite that is under siege.
Park officials cleared brush and set sprinklers on two groves of giant sequoias that were seven to 10 miles away from the fire's front lines.
"We're starting to get a little bit of a handle on this thing," says Lee Bentley of the US Forest Service, "it's been a real tiger. He's been going around trying to bite its own tail and it won't let go but we'll get there."
While sequoias have a chemical in their bark to help them resist fire, they can be damaged when flames move through slowly.
The fire has swept through steep Sierra Nevada river canyons and stands of thick oak and pine, closing in on Tuolumne City and other mountain communities.
It has confounded ground crews with its 300-foot (90-meter) walls of flame and the way it has jumped from treetop to treetop.
The US Forest Service said the fire was threatening about 4,500 structures and destroyed at least 23.
Rugged terrain, strong winds and bone-dry conditions have hampered firefighters' efforts to contain the blaze, which began Aug. 17.
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