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Despite blazing temperatures and difficult terrain, firefighters have increased containment on the Dam Fire which has burned more than 200 acres in the mountains north of Azusa, officials said Friday.

The wildfire erupted Thursday afternoon around 1:45 p.m. in the 9500 block of North San Gabriel Canyon Road, near Morris Dam in the Angeles National Forest, the Los Angeles County Fire Department reported.

As of Friday morning, the Dam Fire had burned 217 acres and was 40% contained. Firefighters are continuing to aggressively work on gaining the upper hand despite sweltering temperatures.

“The combination of hot temperatures, low relative humidities, locally gusty winds, and drying fuels will bring elevated fire weather conditions to the Dam Fire burn area today,” officials said on the wildfire’s InciWeb page.

At around 1:15 p.m., officials said fire activity was increasing south of Morris Dam. In a tweet, the National Forest Service said helicopters were making water drops and crews were working to establish a containment line.

More than 250 firefighters from several agencies responded to the wildfire to battle it from the ground. Video from Sky5 also showed aerial units dousing the flames with water from above. Nearby residents could hear the planes working overhead throughout the afternoon.

The fire grew quickly on Thursday afternoon, resulting in mandatory evacuations and road closures.

 Mandatory evacuations were ordered around 4 p.m. for those in the area north of Morris Dam to Crystal Lake. Camp sites and recreation areas in the surrounding areas are also off limits.

“They are not typical residential evacuations ion that we typically see during these big wildfires,” Marc Peebles of the U.S. Forest Service told KTLA. “There are some special use cabins up there and I believe one of them had people in it so they evacuated the folks out of there.”

Highway 39 was closed to all traffic at Old San Gabriel Canyon Road, as well as East Fork Road. The Azusa Police Department said the closures would be in effect through at least Sunday. Non-residents were not being allowed to go past El Encanto Restaurant.

In addition to the heat wave, rock slides have also made the situation difficult on crews.

“As the slopes burn it loses the ability to hold back those heavy rocks, so we have had several rockslides that have come down on the roadways so CalTrans is here working with us,” Peebles said.

The South Coast Air Quality Management District issued a smoke advisory in effect through Friday afternoon due to the Dam Fire as winds were expected to come from the southwest, which could push smoke to the northeast, toward Wrightwood and Mount Baldy.

The cause of the wildfire remains under investigation.