Crews are taming the Morgan Fire, which has charred an estimated 3,133 acres in and around Mount Diablo State Park since it started Sunday afternoon, Cal Fire officials said.
The fire was at 90 percent containment as of this morning, Cal Fire spokesman Steve Kaufmann said.
Fire crews expect to have the blaze completely contained by Friday, and Thursday a "significant demobilization" of fire crews is planned, he said.
The fire started off of Morgan Territory Road near Mount Diablo State Park, southeast of Clayton, shortly after 1 p.m. Sunday. Since then, more than 1,370 fire personnel from more than a dozen agencies responded to the blaze.
Crews are focused on holding the perimeter around the blaze and ensuring that the winds that tend to blow through the area in the afternoon don't cause any flare-ups, he said.
"Because the humidity is so low, we just want to make sure everything is out before we leave the area," Kaufmann said. "We are being extra cautious."
Since grasses, trees and other fuel in the area were already dried out, the fire was able to spread much more quickly than it would have during a year with more rainfall, he said.
Both in the Morgan Fire and in wildfires throughout the state, he said, "We're seeing fire behavior that's super extraordinary, because it's so dry and those fuel beds are so receptive to fire."
Residents from about 100 houses that were threatened by the fire have been allowed to return home since evacuations were ordered Sunday.
Kaufmann said the Morgan Fire serves as a reminder that residents should be prepared to evacuate immediately in the event of a wildfire before crews arrive in their neighborhoods. Also important, he said, is for residents to secure their homes by closing all windows, doors and garages to prevent fire from spreading to the building.
"When fire is approaching neighborhoods, it's real important for residents to make sure their houses are locked up tight," he said.