(NBC) - A California wildfire that has scorched an area roughly the size of Chicago near Yosemite National Park was 20 percent contained Monday night, officials said — a jump from 7 percent the previous night.
But the so-called Rim Fire, stretching 250 square miles, still threatens 4,500 structures as well as the power and water utilities for San Francisco, roughly 200 miles to the west. It has charred 160,980 acres and was growing rapidly, hampering suppression efforts, authorities said Monday night.
The raging flames also loomed over towering sequoias that are among the largest and oldest living things on the planet. The iconic trees can withstand fire, but brutal conditions — including harsh winds and thick brush — have prompted park employees to take extra precautions in the Tuolumne and Merced groves, according to the Associated Press.
"All of the plants and trees in Yosemite are important, but the giant sequoias are incredibly important both for what they are and as symbols of the National Park System," park spokesman Scott Gediman told the AP.
California Gov. Jerry Brown says he'll ensure his state as the resources available to deal with the state's massive wildfire.
Though the fire remains in a remote wilderness area of Yosemite National Park, it has burned 22,000 acres inside the protected area. Wildlife has been seen on the move, including a mother bear and her cub.
Firefighters were hoping to advance on the flames Monday, but strong winds threatened to push the blaze closer to Tuolumne City and nearby communities. Mandatory evacuations were ordered south of state Highway 120 and north of Old Yosemite Road.
A group of elite firefighters, Strike Team 2276-Alpha from San Mateo County, was tucked into the trees Monday to protect the town of Tuolamne in case the blaze came over the hill.
"It is dangerous," said strike team commander Ron Levezzo. "We had 19 firefighters, hotshots killed in Arizona. Fire is unpredictable when it gets up into the treetops."
"This fire has continued to pose every challenge that there can be on a fire," said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
Almost 3,700 firefighters have been drafted in to tackle the fire that continues to threaten thousands of rural homes surrounding the popular tourist destination.
The fire has already destroyed 23 structures, including all of the popular Berkeley Tuolumne Family Camp, an institution founded in 1922.
"I'm just so sad on so many levels," Janice Lin of Berkeley told NBCBayArea.com. Lin had been going to the camp with her children for years.
Outside Yosemite, Lewis Paden, 80, returned Monday to the site where his father had built a family cabin — all of it now gone.
"We're going to do our best to rebuild it back for the grandkids and great-grandkids to enjoy it," Paden said.
More than 12 helicopters and a half-dozen fixed-wing tankers were dropping water and retardant from the air Sunday.
Gov. Jerry Brown declared a state of emergency Friday for San Francisco, saying the fire had damaged the electrical infrastructure serving the city and forced the Public Utilities Commission to shut down power lines.
President Barack Obama called Brown on Sunday for an update and expressed his "gratitude for the brave men and women working tirelessly to combat this devastating fire," the White House said.
On Sunday, the fire had moved to within 2 miles of the Hetch Hetchy Reservoir, which serves 85 percent of San Francisco with water, according to San Francisco Public Utilities Commission spokesman Tyrone Jue.
At close to 250 square miles, the blaze is more than four times the size of San Francisco.
The fire was sparked last week in a remote canyon of Stanislaus National Forest, with arid conditions feeding the flames.
NBCLosAngeles.com reported that the Rim Fire is the thirteenth-largest wildfire in California's history and one of seven that has burned more than 10,000 acres this summer alone.
Statewide, nearly 9,000 firefighters are battling nearly 400 square miles of fires.