The fire has destroyed 111 buildings, including 31 residences, officials said. About 4,500 homes northwest of the fire and two groves of giant sequoias and other historic landmarks remained threatened.
Officials also said Tioga Road would be closed beginning Wednesday, probably through the the Labor Day weekend.
In a race against the flames, firefighters battled to gain ground on the perimeter as containment remained at 20%, primarily on the southwest flank.
The challenges that firefighters faced on the east were a marked departure from the granite barricades that crews used to the north and the rivers and fire lines that kept the fire at bay on the west.
On the east, officials said, the flames have a relatively flat, clear path into Yosemite National Park, which remained open to tourists Tuesday.
“They’re in scouting mode,” said Dick Fleishman of the U.S. Forest Service. “There’s not a lot of real good areas to get out in there and do a lot of work.”
On Tuesday, firefighters shored up their defensive perimeters — miles long and 12 bulldozer blades-wide swaths of land cleared of brush and vegetation up to the the Tuolumne River — to protect homes near California 108, said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection.
“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.”
The Rim fire has grown to become the seventh-largest fire in state history.
“It’s burning its way into the record books,” Berlant said.
Firefighters who returned to camp after a night of grunt work, building defenses and extinguishing hot spots, looked like raccoons, their faces were blackened with soot and ash but their eyes were clear from the goggles they wore.
The command post is big enough to feed and house about 3,700 firefighters from shift to shift, with about half a dozen tractor-trailers with showers standing by in case firefighters muster the energy to use one after eating but before collapsing to the dirt in an exhausted heap.