GROVELAND, Calif. — The Rim fire spread deeper into Yosemite National Park on Tuesday with flames racing unimpeded to the east even as firefighters shored up defenses for communities on the western edges of the blaze.
The fire was 20% contained by Tuesday evening, with almost all of the containment coming on the fire's southwest edge. On the east, the fire has a relatively flat, clear path farther into Yosemite and the 3,700 firefighters battling the blaze have fewer options to control it.
"They're in scouting mode," Dick Fleishman of the U.S. Forest Service said of fire crews. "There's not a lot of real good areas to get out in there and do a lot of work."
The blaze has destroyed 111 buildings, including 31 residences, and is now the seventh-largest fire in state history, having spread across 281 square miles.
"It's burning its way into the record books," said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
On Tuesday, firefighters bolstered defensive perimeters to the south and west — using bulldozers to clear brush and vegetation from strips of land up to the Tuolumne River to protect homes near California 108, Berlant said.
"We've burned back down the mountain so that if the fire makes the river, jumps the river, that side of the hill is already burned," he said. "We're coming around the corner, catching the western portion of the fire and we'll continue to pinch it off as it goes up to the northern flank."
Officials consider about 4,500 homes north of the fire and two groves of giant sequoias and other historic landmarks still in danger.
The Stanislaus National Forest is taking the brunt of the blaze, with the Groveland Ranger District making up most of the southern flank. The region has been hit hard by fires in the past, the most significant in 1987, which claimed the life of a firefighter.
This week's fire has brought sorrow among the district's employees, who not only recall the past devastation but also begrudge the current damage. The fire burned though an area that had a pending $1-million timber sale, said Maggie Dowd, district ranger in the Groveland Ranger District.
"The economic impacts are real, but we haven't begun to estimate them yet," Dowd said Tuesday from her office in a building shrouded in smoke.
So far, the fire has destroyed two federal campgrounds that had been recently upgraded and a day-use area at Rainbow Pools, Dowd said. At least one historic structure — a cabin that had also been recently refurbished — was destroyed and Forest Service crews are still assessing damage to other structures.
Smoke from the fire is starting to drift into the park's northern areas, but it's unavoidable at the command post.
The blaze is a "campaign fire," crews say, meaning that everyone who joins in the effort knows they are going to be there for days, weeks or even months.
Firefighters who returned to camp to rest looked like raccoons, their faces striped with soot and ash. The command post is big enough to feed and house the thousands of firefighters who are working in shifts, with about half a dozen tractor trailers with showers standing by.
As the blaze stretched into its 11th day, officials received visual confirmation of ash on the surface of Hetch Hetchy reservoir, which supplies water to 2.6 million people in the Bay Area. But officials monitoring water quality have seen no change, said Tyrone Jue, spokesman for the San Francisco Public Utilities Commission.
Hetch Hetchy supplies are drawn from the reservoir at a depth of 260 feet, so there is little chance of contamination, Jue said. More problematic than ash on the surface of the water is the potential for runoff to enter the reservoir when rain comes later in the season, he said.
Gov. Jerry Brown issued a state of emergency for the city and county of San Francisco on Friday because of the threat to the reservoir.
Following standard procedure when the reservoir is threatened, additional water is being pumped to reservoirs in Alameda and San Mateo counties, which also supply Hetch Hetchy customers, Jue said. The amount of water being transferred has been increased from 275 million gallons a day to 302 million gallons as a precaution, the utility's commission said.
Crews have also repaired one of two hydroelectric power stations shut down by the fire, and they are in the process of assessing the damage to the second unit, Jue said.
Supplemental power has cost about $600,000 since the two power stations were taken offline Aug. 17, the day the Rim fire started.
Times staff writer Diana Marcum contributed to this report.