State fire spokeswoman Alicia Amaro says the fast-moving blaze began shortly before noon Tuesday in the Pope Valley area.
By 2 p.m., the fire had burned 200 acres and 500 by 3:30 p.m. as it spread toward the east as firefighters from the state, Napa, Lake and Solano counties continued working in temperatures approaching 90 degrees.
State fire spokeswoman Karen Stasko also says that some residents living in a nearby subdivision have been evacuated as it is not immediately known how many.
Five structures have also been damaged.
Stasko adds that no injuries have been reported. The cause of the fire also has not yet been determined.