(CBS News) YOSEMITE NATIONAL PARK - In the nine days since the Rim Fire near Yosemite National Park began, nearly 150,000 acres have burned and the blaze has grown to the 13th largest fire in California's history. More than 3,000 firefighters have battled gusty winds and dry brush to contain 15 percent of the massive fire.
The blaze now threatens San Francisco, 130 miles to its west as it burns closer to the Hetch Hetchy Reservoir, which supplies 85 percent of the city's drinking water. California Gov. Jerry Brown declared a state of emergency for San Francisco over the weekend.
According to Glen Stratton, an operations chief on the fire suppression team, the danger now is ash getting into the water.
"That's a huge concern, a safety concern if the water gets contaminated," Stratton told CBS News. "We're paying real close attention to our operations at that facility up there."
Stratton estimated that at its current rate, the fire could reach the reservoir within a matter of days. But he remained confident that the reservoir could be kept safe.
There are also economic concerns. About 20,000 acres are burning in Yosemite, which pumps about $400 million into the economy. A major attraction are the majestic groves of 2,000-year-old Sequoia trees. Crews are hosing them down to weaken the intensity of the encroaching blaze.
"A low intensity burn around the bases won't be bad," Yosemite superintendent Don Neubacher told CBS News. "Some of the seedlings need fire to regenerate, so if we can keep it to low intensity burns, it can actually help the sequoias."
He added: "We are going to use the fire to potentially enhance the groves. And the only thing we have to ensure is that we don't get a high intensity catastrophic fire."
Winds from the south are pushing the fire toward the northwest side of the park, a potentially positive development. As the fire moves north and east, it will run into solid granite stretches with little fuel to burn. The fire won't be out completely until winter.