Firefighters hoped to continue making progress Tuesday on the Rim fire near Yosemite National Park, which has already burned through more than 160,000 acres but was 20% contained.
The fire was threatening 4,500 homes Monday night.
A persistent air attack Monday helped firefighters make progress in their battle to stop the westward spread of the massive fire, officials said.
Helicopters and fixed-wing aircraft, including huge DC-10 bombers filled with fire retardant, made repeated assaults near Tuolumne, in an area that fire officials have referred to as the California 108 corridor on the western flank of the blaze.
Officials said crews on the western edge were also conducting backfiring operations, a dangerous tactic in which firefighters burn vegetation inside a fire line to help contain a rapidly spreading blaze.
The blaze that broke out Aug. 17 was still spreading to the north and northeast into old growth timber in the Stanislaus National Forest, the U.S. Forest Service said.
The flames have also raged into Yosemite, burning nearly 22,000 acres of parkland, officials said.
At least 23 structures have been destroyed.
Temperatures in the Yosemite Valley region were expected to remain in the mid-90s this week. Officials at Yosemite said campgrounds have been packed and that the popular Yosemite Valley and much of the park are free of smoke.
On Monday, San Francisco officials scrambled to send more water to the metropolitian area as the fire rained ash on the reservoir that serves as its chief source of water, the Associated Press reported. Officials hoped to make the transer before the water became tainted.
Utility officials monitored the clarity of the Hetch Hetchy Reservoir and used a massive new $4.6-billion gravity operated pipeline system to move water quickly to reservoirs closer to the city, the AP reported.
The Hetch Hetchy supplies water to 2.6 million people in the San Francisco Bay area, 150 miles away.
The fire also destroyed the Berkeley Tuolumne Family Camp near Groveland.
ALSO:Copyright © 2015, The Baltimore Sun