The fire has burned an estimated 3,133 acres since it was first reported around 1 p.m. Sunday off of Morgan Territory Road near Mount Diablo State Park, southeast of Clayton.
Cal Fire had previously reported a higher acreage, but after surveying the fire site, the agency reduced its estimate of the fire's size.
Evacuations had been ordered Sunday, and as many as 100 homes were threatened by the flames, according to Cal Fire. On Tuesday evening, the evacuation orders were lifted and all residents were able to return home.
Roads on the eastern side of the mountain that had been closed because of the fire have reopened, according to Cal Fire.
Three firefighters suffered minor injuries battling the blaze, and one communications shed was destroyed, Cal Fire officials said.
More than 1,370 fire personnel from more than a dozen agencies responded to the fire. Crews were starting to leave the area this morning as the fire died down.
A smoke advisory issued by the Bay Area Air Quality Management District remains in effect today, air district spokesman Tom Flannigan said.
He said the advisory would likely remain in effect "as long as there are flames."
The advisory is a reminder for residents, especially those in Contra Costa and Alameda counties, that air quality is compromised by smoke from the blaze.
The air district has advised residents, especially those with respiratory problems, to limit their outdoor exposure.
Flannigan said there have been no reports of residents suffering health problems because of the smoke.