Groveland:
Officials are clearing brush and setting sprinklers to protect two groves of giant sequoias as a week-old wildfire rages along the remote northwest edge of Yosemite National Park.
The iconic trees can resist fire, but dry conditions and heavy brush are forcing park officials to take extra precautions in the Tuolumne and Merced groves. About three dozen of the giant trees are affected.
"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 on Saturday.
The trees grow naturally only on the western slopes of the Sierra Nevada and are among the largest and oldest living things on earth.
The Tuolumne and Merced groves are in the north end of the park near Crane Flat. While the Rim Fire is still some distance away, park employees and trail crews are not taking any chances.
The fire was well into the northwest corner of the park, the U.S. Forest Service said.
More than 5,500 homes are threatened. Four were destroyed, though officials say the number could go up once they can safely assess burned areas.
Jessica Sanderson said one of her relatives gained access to the family's property in Groveland, just 26 miles (41 kilometres) from the park's entrance, on Saturday and was able to confirm their vacation cabin had burned to the ground.
The family saw firefighters on a TV news report a day earlier defending the cabin.
"It's just mind-blowing the way the fire swept through and destroyed it so quickly," said Sanderson, who's been monitoring the fire from her home near Tampa Bay, Florida. "The only thing left standing is our barbeque pit."
The Rim Fire has burned nearly 200 square miles (518 sq. kilometres) - an area about the size of Chicago. It started in a remote canyon of the Stanislaus National Forest Aug. 17 and is just 5 per cent contained. Its cause was under investigation.
The fire has grown so large and is burning dry timber and brush with such ferocity that it has created its own weather pattern, making it difficult to predict in which direction it will move.
"As the smoke column builds up it breaks down and collapses inside of itself, sending downdrafts and gusts that can go in any direction," said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection. "There's a lot of potential for this one to continue to grow."
The tourist mecca of Yosemite Valley, the part of the park known around the world for such sights as the Half Dome and El Capitan rock formations and waterfalls, remained open, clear of smoke and free from other signs of the fire that remained about 20 miles (32 kilometres) away.
More than 2,600 firefighters and a half dozen aircraft were battling the blaze.
The fire is burning toward the Hetch Hetchy reservoir, where San Francisco gets 85 per cent of its water, and power for municipal buildings, the international airport and San Francisco General Hospital. Gov. Jerry Brown declared a state of emergency because of the threats.
Officials with the San Francisco Public Utilities Commission were running continuous tests on water quality in the reservoir that is the source of the city's famously pure water.
Deputy General Manager Michael Carlin told The Associated Press on Saturday that no problems from falling ash have been detected.
The commission also shut two hydro-electric stations fed by water from the reservoir and cut power to more than 12 miles of lines. The city has been buying power on the open market.
A 4-mile (6.4-kilometer) stretch of state Route 120, one of three entrances into Yosemite on the west side, remained closed Saturday. Two other western routes and an eastern route were open.