Evacuations are in effect for the area around Curry Creek Road and Oak Hill Road.
The fire is burning in an area along Morgan Territory Road in Mount Diablo State Park.
Cal Fire reports the fire has doubled in size during the past hour, growing from 170 to about 350 acres. Several fire departments are assisting Cal Fire.
The fire is only 10 percent contained.
Some people have tweeted that ash is falling on Clayton.
Stay with ABC7 News for the latest details on this developing story.
