The fire in the San Jacinto Mountains grew to around 24,818 acres - roughly 39 square miles - and was 15 percent contained, U.S. Forest Service spokeswoman Kate Kramer said.
About 6,000 people remained evacuated for a third day as the fire spread in three directions amid the rugged, timbered ridges. Some communities on the eastern edge of the fire were reopened to residents, but about 4,100 homes remained under potential threat.
The fire was only about two miles from Idyllwild on its western flank and the same from Palm Springs, down below on the desert floor. However, it was burning relatively slowly with the most active area south of town.
An enormous plume of smoke could be seen from Palm Springs.
Popular campgrounds, hiking trails and a 30-mile section of the Pacific Crest Trail that runs from the Mexican border to Canada, remained closed.
Some 3,300 firefighters, aided by nearly 30 aircraft, battled the fire, which stretched from 4,000 feet to 9,000 feet along the mountains. For that reason, crews could be working in temperatures ranging from a comfortable 75 to a scorching 110 degrees.
Kramer said a storm front was heading toward the region, bringing a 20 percent chance of rain but also 15-24 mph winds with gusts to 40 mph that could push the flames in erratic ways.
"That's the double-edged sword of having a front move in," she said. "It can cause some very unpredictable weather."
The fire, which began Monday afternoon, has burned six homes and mobile homes, one cabin, and more than a dozen other buildings. One home also was damaged.
Idyllwild resident Dave Jones was back in his Southern California home on Thursday, a day after evacuating, but remained ready to leave.
The walls were bare in the home where he's lived for the past 40 years after the 64-year-old and his wife stowed the valuable mementos, along with more practical items, like clothes, jewelry, medicines and the computer hard drive before heading to their son's home in nearby Hemet.
"The fire came right up by the ridge yesterday afternoon, gave everybody a pretty good scare that it was going to come down the hill," Jones said Thursday night.
The last time he evacuated for a fire it was 1997, and he stayed away for four days. Jones said he considered the order he got Wednesday "a light evacuation" and wasn't afraid because he knows of a controlled dirt road to use as "an escape route" if fire does come down that ridge.
Authorities said the fire was "human-caused" but they wouldn't say whether it was accidental or intentional. There have been no reports of any injuries.
The fire was about 12 miles from the site of the 2006 Esperanza wildfire that killed five U.S. Forest Service firefighters and destroyed 34 homes and burned an area that hadn't burned in many years.
AP reporters Raquel Maria Dillon in Idyllwild and Shaya Tayefe Mohajer in Los Angeles contributed to this report.