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Firefighters were working in steep, mountainous terrain on Monday, seeking to fully contain a wildfire that had destroyed homes and prompted the evacuation of thousands of residences after breaking out in the foothills above Glendora.

More than 800 fire personnel were working on the Colby Fire Monday. Here, members of a U.S. Forest Service clear brush on a hillside above Highway 39 on Jan. 17, 2014, in Azusa. (Credit: Getty Images)

On the fifth day of the firefight, the Colby Fire was estimated at 1,952 acres and 84 percent contained, according to a unified command spokesman.

Crews were deep in the Angeles National Forest, focusing on the northeast and northwest edges of the fire on Monday, said Marc Peebles, spokesman for Southern California Incident Management Team 3.

“They’re making good progress, it’s just that it’s real slow,” Peebles said.

More than 800 firefighters and other personnel remained working on the Colby Fire Monday, he said, “doing a lot of heavy mop up in some pretty steep, nasty areas.”

The blaze broke out just before 6 a.m. Jan. 16 in the Glendora foothills and spread rapidly westward in dry brush amid unseasonably high temperatures, a red flag warning and a statewide drought.

Three men in their 20s had been taken into custody on suspicion of recklessly setting a fire. They said their campfire got out of control, according to Glendora’s police chief, who reported that the threesome would face federal charges.

Five homes and 10 outbuildings were destroyed, while seven homes and one outbuilding were damaged, according to the interagency website InciWeb.

The last remaining evacuation orders were lifted on Saturday evening for residents in the Mountain Cove area of Azusa. Highway 39 — also called San Gabriel Canyon Road — remained closed Monday.

Full containment was expected 6 p.m. Wednesday, Peebles said.