William Cummings, USA TODAY
The raging wildfire burning through a remote section of Yosemite National Park has gained strength, threatening nearby communities as well as water and electrical resources for San Francisco.
High winds were poised to fan the flames further north into the park Sunday.
"The wind could push it further up north and northeast into Yosemite and closer to those communities and that is a big concern for us," said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
The fire is reported to be 203 square miles. Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias threatened by the blaze. The trees grow naturally only on the western slopes of the Sierra Nevada and are among the largest and oldest living things on earth.
"All of the plants and trees in Yosemite are important, but the giant sequoias are incredibly important both for what they are and as symbols of the National Park System," park spokesman Scott Gediman said.
The "Rim" fire has not yet moved into any of the heavily-traveled tourist areas of Yosemite. The valley that is home to the park's iconic sites such as Half Dome and Yosemite Falls remains open and clear of smoke.
Although the park remains open, hundreds of residents and visitors have already fled the area and authorities have canceled a popular bluegrass music festival planned for Labor Day weekend.
Fueled by dry brush and undergrowth, the fire has burned more than 125,000 acres of towering pine and oak, becoming one of the largest blazes in California history. It is only 7% contained, despite the efforts of 2,672 firefighters backed by planes and helicopters and at least 4,500 residences remain in danger.
"A major effort" intended to hold the fire east of the North Fork of the Tuolumne River is underway, according to CalFire. Resources are also being focused on the fire's eastern edge in Yosemite National Park, "to minimize impacts to our national treasure."
Governor Jerry Brown declared a state of emergency for San Francisco as the fire threatened the city's water and electrical resources in Tuolumne County.
San Francisco Public Utilities Commission officials are running continuous tests on water from the Hetch Hetchy Reservoir. Deputy General Manager Michael Carlin told the Associated Press he fears ash could fall into the reservoir, causing a federal water quality violation.
The Hetch Hetchy watershed supplies famously pure and clear water to San Francisco's 2.6 million consumers. About 85% of the city's water travels 160 miles from the Hetch Hetchy Reservoir.
The commission shut two hydro-electric stations fed by water from the Hetch Hetchy and cut power to more than 12 miles of lines. Electricity from those lines powers the San Francisco General Hospital and the international airport.
Contributing: The Associated Press