The fire grew Wednesday evening to more than 192,000 acres, or 301 square miles, and became the 6th largest wildfire in California history, state fire officials said. The blaze was 30% contained.
But the rate of the fire's spread had slowed considerably since last week, and officials were expecting full containment by Sept. 10, the California Department Forestry and Fire Protection said.
Fire officials credited cooler temperatures, higher relative humidity and lighter winds with helping crews make progress toward containing the blaze, which has been burning since Aug. 17.
"That's given us a greater opportunity to get in there and strengthen our containment lines," Cal Fire spokesman Daniel Berlant told The Times.
He also credited backfiring operations with helping strengthen containment lines near Tuolumne city on the northern flank of the blaze.
Firefighters were also planning to conduct backfire operations on the southeastern edge of the fire in Yosemite, the U.S. Forest Service said.
The tactic involves setting fires inside containment lines to burn vegetation in the path of advancing flames and stop or slow the spread of the blaze.
Fire officials also used a National Guard drone to provide aerial images of the blaze and give fire commanders real-time information on fire activity and resource deployment, officials said.
The drone, about the size of a small Cessna plane, takes off from the Victorville Airport and is operated from March Air Reserve Base in Riverside, said Lt. Col. Tom Keegan of the National Guard.
The aircraft is ideal for a blaze such as the Rim fire, which covers a large area, much of it inaccessible terrain.
"This was a perfect fire to use this technology to get an eye in the sky," Berlant said.