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 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 percent 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.
"We've had other fires in the watershed and have procedures in place," he said.
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 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.