The giant wildfire burning at the edge of Yosemite National Park is about 20 per cent contained.
The US Forest Service says the fire has now consumed 758 square kilometres.
The fire in northern California has destroyed 111 structures and threatened water supplies, hydroelectric power and giant sequoia trees – a state icon.
Some 4500 structures remain threatened.
The fire, one of the largest in state history, has caused air pollution problems in California cities far from the scene.
Forestry experts say unnaturally long intervals between wildfires and years of drought have primed the Sierra Nevada mountains for the explosive fire in the rugged landscape.
Federal forest ecologists say historic policies of fire suppression to protect timber interests left a century’s worth of fuel in the fire’s path.
Two years of drought and a constant slow warming across the Sierra Nevada also worked to turn the Rim Fire into an inferno.
For years, forest ecologists have warned that Western wildfires will only get worse.