(NECN/NBC News: Jay Gray) - Firefighters are working around the clock to gain control of a wildfire threatening Yosemite National Park.
The fire has already burned 200 square miles of forest over the past week and is less than 10 percent contained.
Strong afternoon winds continue to push the flames of the massive rim fire, and the limits of more than 2,500 firefighters along the front lines.
"The terrain is steep," said Ashley Taylor of U.S. Forest Services. "The crews are out there working hard, and some areas just can't even be accessed".
Still, the fire continues to force its way into those areas, climbing the rugged mountains, racing through the valleys, threatening more than 4,000 homes.
Nervous residents can only watch and worry where it might go next.
"What happens when it gets up on here, it'll make a run," said retired firefighter Robert Quinlan. "This will make an in run into Sonora."
Hot shot teams are guarding communities on the ground. A half dozen aircraft are targeting hotspots from the air, including an area near the Hetch Hetchy Reservoir in Yosemite National Park, which provides water and hydroelectricity to San Francisco.
With the flames now less than four miles away, Governor Jerry Brown has declared a state of emergency for the city.
"It's quite possible that it could reach the Hetch Hetchy with its movement," said Tom Medema, spokesman for Yosemite National Park.
Also in jeopardy is a section of three dozen ancient sequoias. Though right now, the fire appears to be turning away from the trees, but still running in multiple directions, out of control, and swallowing everything in its path.