GLENDORA Calif. -

The last residents affected by evacuation orders due to the Colby Fire north of Azusa and Glendora headed home today as firefighters announced more progress in encircling the blaze, which is expected to be fully contained by Wednesday.

The fire was 61 percent contained, having burned 1,906 acres while destroying five homes and damaging 17 other structures, officials said.

Residents of the Mountain Cove subdivision north of Azusa were allowed to return to their homes at 6 p.m., just as Red Flag Warnings expired, according to the Los Angeles County Sheriff's Department.

Full containment -- originally expected for Sunday -- was pushed back to Wednesday, Nathan Judy of the U.S. Forest Service said.

``Everything is fluid,'' Judy said, adding that firefighters set backfires today and worked to extend and fortify containment lines. ``We have to get boots all the way around this fire to call this thing completely out.''

Judy said firefighters are dealing with steep, sometimes inaccessible terrain.

``We want to make sure everyone is safe before they go in there,'' he said.

The fire was allegedly set by a trio of young men tossing papers into a campfire at 5:50 a.m. Thursday near Glendora Mountain Road.

Heavy smoke from the blaze also sparked concerns about poor air quality, especially for people with existing respiratory issues, according to the Air Quality Management District officials. People in affected areas were urged to stay indoors with air conditioning.

About 1,175 personnel were on the fire lines, along with nine helicopters and two SuperScooper aircraft.

The three people injured included a woman who was hit by a burning palm frond that fell on her back. One firefighter suffered an ankle injury that did not require hospitalization, and an other was taken to a hospital for treatment of a minor burn.

Clifford Eugene Henry Jr., 22, of Glendora; Jonathan Carl Jarrell, 23, Irwindale; and Steven Robert Aguirre, 21, a transient last known to live in Los Angeles, remained jailed in lieu of $500,000 bail on suspicion of recklessly starting a fire. The men might face federal charges because the fire started on U.S. Forest Service land, but the U.S. Attorney's Office said no charges had been filed as of Friday.