The wildfire, burning an average 300 acres an hour in the central Sierra Nevada region, down from 1,000 acres an hour Tuesday, is now 30 percent contained, up from 23 percent contained midday Wednesday and 20 percent the day before, California Department of Forestry and Fire Protection spokesman Daniel Berlant said.
Full containment is expected by Sept. 10, he said.
"A lot of that has to do with the fact that the weather is cooperating a lot more with us," Berlant told the San Jose (Calif.) Mercury News, noting temperatures have cooled and humidity has risen.
Berlant said the constant air drops and bulldozer-dug dirt lines around the perimeter of the fire have paid off.
"There's a lot of work that's been done over the past week and a half now to really put this fire to bed," Berlant said. "We are hoping that we've turned the corner."
Still, the gigantic wildfire -- California's sixth-largest in history and the nation's largest -- has devoured nearly 195,000 acres, or 305 square miles, and threatens ancient giant sequoias, also known as giant redwoods.
The amount of acreage blackened by Wednesday morning was 187,000, up from 184,000 the night before and 179,000 Tuesday morning.
At least 111 structures, including 31 residences, have been destroyed in the blaze and more than 4,500 residences remain threatened.
Three firefighters were reported to have suffered minor injuries.
The firefighting cost has topped $39 million.
The fire, which has charred more than 40,000 acres, or 63 square miles, of Yosemite National Park, relentlessly burned the southern and western shores of Yosemite's 117 billion-gallon Hetch Hetchy Reservoir, dropping ash into the source of water for 2.6 million Bay Area residents and businesses, from San Francisco south to Silicon Valley.
The water's quality has not been compromised, officials have said.
Firefighters worked to protect the reservoir's infrastructure from being damaged by the blaze, they said.
The California National Guard said Wednesday it launched an MQ-1 Predator drone, often used by the U.S. Air Force and CIA to fight terrorism, to gather data about the fire for firefighters.
The Predator carries cameras and sensors.
"It gives them a great amount of insight and information as far as understanding where the fire is most intense and how they can best approach it," Capt. Will Martin told the Mercury News.
"That's an advantage we don't have as far as being able to fly [human-operated aircraft] into the more dangerous areas of the fire," he said.
The drone is operated remotely from March Air Reserve Base near Riverside, Calif.
The cause of the Rim fire, which started Aug. 17, remains under investigation.