The fire was reported at about 11:20 a.m. off of Bailey Road in an unincorporated area between Pittsburg and Concord, Contra Costa County Fire Protection District Marshal Lewis Broschard said.
As of 1:30 p.m., the two-alarm blaze had been contained but firefighters were still working to control it.
No homes were threatened and no structures have burned, Broschard said.
The cause of the fire has not yet been determined.
Contra Costa County firefighters are being assisted by Cal Fire and federal firefighters from the Military Ocean Terminal Concord, Broschard said.