Cal Fire says forward progress is stopped and containment is at 40%.
It broke out just before 5 p.m. at 10 acres and burned about 40 acres, according to Contra Costa Fire.
No injuries or threatened structures have been reported but steep terrain made it difficult for firefighters to get to the flames.
The cause of the fire is still under investigation.
Stay with ABC7 Eyewitness News for the latest details on this developing story.
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