Little wind and lots of humidity aided firefighters in containing a 500-acre blaze late Friday and early Saturday on the north side of Mount Diablo State Park outside Clayton.
The fire broke out about 8 p.m. Friday near an abandoned trailer on Bragdon Way, near where Marsh Creek and Morgan Territory roads intersect. It quickly ignited the grass, said Chris Morgan, a spokesman for the California Department of Forestry.
Firefighters from CDF, Contra Costa Fire and San Ramon Valley Fire also moved quickly to contain the fire burning in the steep, thick, dry grass.
The fire was contained at 3:35 a.m. Saturday and was supposed to be completely out sometime today, Morgan said. "It's looking real good right now out there."
At its height, 300 firefighters and support staff were on scene working to keep the fire from spreading, Morgan said. But while many of the crews have left, others remained Saturday night and today to make sure no flare ups occurred.
Friday night, low winds, 93 percent humidity and quick work by crews kept the fire from charring more land in the area.
"It could have been a lot worse" had the winds picked up or had the air remained dry, Morgan said.
At one point, seven homes on Bragdon Way were threatened because of their proximity to the fire, but because the owners had done a good job clearing brush away -- making "defensible space" -- the homes were safe, Morgan said.
CDF inspections have been ongoing and will continue for homes in the Clayton and Morgan Territory areas.
Investigators were still trying Saturday night to determine the cause of the fire, a task that may take several days, Morgan said.
Fire season is officially under way in Contra Costa County. Several major grass fires have plagued the unincorporated areas. Wednesday, firefighters from several agencies battled a 250-acre grass near a windmill farm on Vasco Road near the Byron airport. On June 5, crews battled a 1,000-acre fire in Byron. A fire truck on its way to that fire collided with a Toyota Corolla, which collided with another van. One woman in the passenger seat died and the driver and the other passenger were sent to area hospitals. Two children in the car were taken to Children Hospital with minor injuries.