Spokesman Robin Mario for the Northwest Interagency Coordination Center told The Oregonian that some 240 firefighters have responded to the Box Springs blaze.
Thunderstorm activity was being blamed for causing small wildfires in both Oregon and Washington.
The entire eastern half of Washington is under a red flag warning due to the threat of dry lightning, KING-TV in Seattle reported.
"We could be digging in the ground for days on end," said Monroe firefighter Capt. Ron Adams.
Adams said he is prepared to spend weeks fighting fires on the east side of the state.