Crews arrived at the scene at Vasco Road and North Vasco Road on the north side of Interstate Highway 580 at 10:16 a.m., Daniel Berlant said.
Firefighters have stopped the spread of fire and no structures are in danger. At one point there was a structure at risk, but Berlant said it was in a very remote area and fortunately it did not catch fire.
"With the high temperatures and low humidity, the fire was able to rapidly spread," Berlant said.
The cause of the fire is still under investigation.
Berlant said crews would be on the scene all afternoon working on containment and mop up.