The fire, named the Mind Fire, was first reported at 2:18 pm on Mines Road in Livermore.
At first fire officials said it was moving uphill, at a moderate to dangerous rate of speed.
An aircraft has since "made good progress slowing down the fire," and "retardant has been applied around the perimeter, according to Cal Fire.
Ground resources are now on the scene.
Stay with ABC7 News for the latest details on this developing story.