The Fern Fire was contained to 1.5 acres burned near Boulder Creek in Santa Cruz County after breaking out Monday, Cal Fire said.
The fire started at 4:45 in a wooded area west of Highway 9 and near Fern Drive.
The hilly, densely wooded terrain "was difficult to access," Cal Fire said.
Five Cal Fire engines and two helicopters attacked the flames. Firefighters also came Boulder Creek and Ben Lomond to help.
The cause of the fire is under investigation.
A red flag warning has been issued because conditions make it easy for wildfires to ignite, but this area was not covered by the warning. That warning covers areas near Sacramento, including parts of Solano County.