CONCORD -- Fire investigators on Tuesday were trying to determine what sparked a three-alarm blaze that burned a hillside near a major route connecting east and central Contra Costa County, but said another fire near Brentwood was suspicious.

The two fires on Monday combined to burn more than 500 acres of grassland, but nobody was seriously injured, said Steve Aubert, a spokesman for the Contra Costa Fire Protection District. One firefighter from the Cal Fire agency suffered a minor injury fighting the Brentwood blaze but did not require hospitalization, Aubert said.

Crews remained at a charred hillside along Kirker Pass Road into early Tuesday afternoon, monitoring hot spots, Aubert said. That fire, which crews were alerted to around 1:15 p.m., scorched approximately 350 acres and was smaller than originally thought, Aubert said.


View Kirker Pass Road Fire in a larger map

The blaze forced the closure of Kirker Pass Road until after midnight. The road is a critical artery running from Pittsburg and past the Sleep Train Pavilion, where it becomes Ygnacio Valley Road and continues into Walnut Creek. It is expected to be utilized even more by commuters affected this week by an ongoing BART strike.

Two sheds and a barn were fully engulfed in the blaze, which hopped a ridge and briefly threatened homes in Pittsburg, Aubert said. The fire was fully contained by 6:45 p.m., Aubert said.

Investigators were still trying to determine the cause of the blaze, Aubert said, but spokesman Robert Marshall said Monday that power lines were "down all over the place." It's not yet known whether the power lines sparked the blaze or were downed by it, Aubert said.

Another fast-moving blaze in Brentwood burned approximately 247 acres, Chief Hugh Henderson of the East Contra Costa Fire Protection District said. It was fully contained by 3:30 p.m., Aubert said.

Witnesses told investigators they saw the beginning of the fire and that it appeared tied to someone using a lawn mower. Investigators characterized the blaze as suspicious, Aubert said.

Also Monday, Moraga Orinda Fire District crews put out a wildfire that burned 1 1/2 acres on Grizzly Peak in Moraga's Tilden Park. Nobody was injured. Crews reported the fire contained at 10:24 p.m. -- 63 minutes after they were called to it, MOFD spokesman Darrell Lee said.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.