By Steve Gorman

LOS ANGELES (Reuters) - Faulty electrical equipment sparked the 10-day-old forest fire that had threatened the scenic mountain resort of Idyllwild in Southern California before cooler, rainy weather helped crews largely subdue the blaze, fire authorities said on Thursday.

The so-called Mountain Fire charred 27,000 acres in mountains near Palm Springs, forcing the evacuation of several communities and destroying seven homes.

The blaze, which was first reported on July 15, was 92 percent contained by Thursday evening, authorities said, as crews worked to mop up hot spots.

The faulty equipment that led to the fire was on private property, on a customer's side of an electrical meter, the California Department of Forestry and Fire Protection said.

The agency said investigators were still trying to learn more details about how the fire started.

About 3,400 firefighters worked for more than a week against the fierce blaze, which roared through dry brush and timber in the rugged San Jacinto mountain range.

The blaze, which ranked for several days as federal fire managers' top priority among 17 large wildfires across several western states, erupted in the San Bernardino National Forest, about 100 miles east of Los Angeles.

The San Jacinto range overlooks Palm Springs, Cathedral City, Rancho Mirage and several smaller desert towns to the northeast, but the main threat was to the village of Idyllwild, a popular vacation destination in the mountains.

The mile-high community, known for its hiking trails, rock climbing and arts and music scene, was ordered evacuated last week, along with the neighboring town of Fern Valley and surrounding parks and campgrounds as flames advanced.

Authorities estimated that some 6,000 residents, campers and other seasonal visitors had been chased out by the fire.

The famed Palm Springs Aerial Tramway, a rotating gondola that carries visitors from the desert floor to an observation post near the San Jacinto peak, was also closed when the fire was raging last week.

Experts say this year could bring one of the worst U.S. fire seasons ever. In recent weeks, a Colorado wildfire ranked as that state's most destructive on record ravaged more than 500 homes and killed two people. In Arizona, 19 members of an elite "hotshot" crew died while battling a fire on June 30.

(Reporting by Steve Gorman; Editing by Sharon Bernstein and Mohammad Zargham)