YOSEMITE NATIONAL PARK, Calif., Aug. 26 (UPI) -- Firefighters in California said Monday the massive Rim fire raging in Stanislaus National Forest was 20 percent contained.
Thousands of people face mandatory or advisory evacuation orders for the fire, currently the largest wildfire burning in the United States, officials said.
In Tuolumne City, firefighters dug trenches, cleared brush and set backfires during the weekend in an attempt to steer the massive blaze away from the 1,600 homes there, the Los Angeles Times reported Monday. Residents are under voluntary evacuation orders.
Residents of Ponderosa Hills were also advised to leave. Parts of Groveland were evacuated Friday.
The fire had devoured more than 265 square miles as of Monday and was only one ridge line away from Tuolumne City, a foothill community about 60 miles northeast of Modesto, USA Today reported.
Firefighters said the Rim fire was so hot it could propel sparks more than a mile and a half -- possibly allowing the fire to jump lines and start new hot spots.
More than 3,400 firefighters from across the state and as far away as Florida were battling the fire, which started Aug. 17 east of Groveland.
The state Department of Forestry and Fire Protection deployed nine helicopters.
Crews were keeping a watchful eye on changing winds, particularly in light of what happened shortly after the fire was first observed, the Los Angeles Times reported.
U.S. Forest Service spokesman Lee Bentley said "things looked good" after an air team dropped water on the fire -- but winds picked up the next day.
"The fire came boiling out, just cooking," Bentley said. "It was so hot it created its own weather. It was like dropping a boulder in a pond; fire spread out in every direction."
A key priority was preventing the fire from spreading further in Yosemite National Park, internationally recognized for its spectacular granite cliffs, waterfalls, clear streams, giant sequoia groves and biological diversity.
The fire has burned some Yosemite acreage, but is still about 20 miles from the most-visited area of the park, the Yosemite Valley, which was not immediately threatened, officials said.
California Gov. Jerry Brown declared a state of emergency for San Francisco and San Francisco County Friday after the fire -- whose flames were leaping across treetops, creating a "crown fire" -- damaged the Bay Area power infrastructure and threatened the Hetch Hetchy reservoir, San Francisco's main water source, serving 2.6 million customers, or 85 percent of the city's water supply.
The fire's fast growth began to slow, officials said late Sunday.
"We are making good progress," state forestry spokesman Daniel Berlant told the San Francisco Chronicle. "It hasn't grown at the rate it did earlier."
Officials said the fire tripled in size from Wednesday to Thursday and then doubled again from Thursday to Friday.
State and local officials prepared for the possibility of new evacuations elsewhere and disruptions to public utilities as the fire burned north and east in extremely dry conditions and hot weather.
The fire had destroyed 23 structures so far.
President Obama was updated on the fire Sunday during a phone call with the governor. The White House said the president "expressed his gratitude for the brave men and women working tirelessly to combat this devastating fire" and reiterated his commitment to providing needed federal resources to support the ongoing state and local response.