GWEN IFILL: Thousands of firefighters pushed today to make headway against one of the largest fires in California history.
Jeffrey Brown has the story.
JEFFREY BROWN: By air and by land, an all-out assault on the enormous Rim fire is raging in the Western Sierra Nevada mountains.
MAN: It's pretty impressive. It's look like a really coordinated effort.
JEFFREY BROWN: The fire has consumed some 235 square miles of California forest since it flamed into life more than a week ago. The big blaze is burning at the Northwestern edge of Yosemite National Park.
KEN PIMLOTT, Cal Fire: We are facing record dry fuel conditions across this state. That has led to well above average the number of fires since the beginning of May, and with this fire and others, we're certainly in -- stretching the number of acres in record that we have burned.
JEFFREY BROWN: Some 360 firefighters managed today to extend containment lines to 15 percent of the fire. They face the challenges of rugged, parched terrain, as well as high winds that whip the fire from ground to treetops, created so-called crown fires.
MAN: Knowing exactly where it's going to go with the wind is a little unpredictable.
JEFFREY BROWN: Another unpredictable factor, whether the fire could reach out to affect San Francisco, nearly 200 miles away.
On Friday, Governor Jerry Brown declared a state of emergency after flames damaged transmission lines that route electrical power to the city. Also at risk, the Hetch Hetchy reservoir, source of 85 percent of the city's water supply.
The fire crept to within one mile of the facility today, but despite ash flakes raining down, officials maintained water quality has not been affected. Still, Governor Brown warned today the effects may show up when the winter rainy season comes.
GOV. JERRY BROWN, D- Calif.: When you burn down everything, you have got a moonscape out there that -- where floods can contaminate the waters.
JEFFREY BROWN: In terms of property damage, the fire has destroyed relatively few buildings and several small towns are under threat. One exception, the Tuolumne Family Camp near the town of Berkeley. The 90-year-old refuge for tourists and local residents burned to the ground over the weekend.
MAN: The fire climbed up into the trees and made a run into the camp. The camp was pretty overgrown. There was of lot of flammables in there. There's a lot of summer tents flammable with fabric and stuff like that. So, it was -- I would imagine they had their hands full.
JEFFREY BROWN: Elsewhere, residents made their way to Red Cross evacuation centers.
WOMAN: You know, you just cry and laugh with everybody else. It's sad. You never think you're going to be here in the situation, and when you watch other people on TV that you can't help that are in it, and then when it hits home, wow.
JEFFREY BROWN: As for Yosemite, the majority of the park with its majestic vistas and waterfalls remains relatively unaffected.
While some back country hiking has been closed, the popular Yosemite Valley area to the south remains open to visitors and campers. Some of the firefighters working to contain the blaze are trying to protect two groves of the park's famous giant sequoias estimated to be 2,000 years old.