The fire was reported around 1:30 p.m. in the 1200 block of Studebaker Drive. Crews got the fire under control, but not before it heavily damaged the garage and spread into the attic of the house.
Officials say the fire started while the homeowner was trying to clean up spilled gasoline in a boat parked inside the garage.
No one was injured in the fire. Crews were able to rescue a cat uninjured from the building's crawlspace.
Damage has been estimated at $165,000.
Firefighters from the Walla Walla Fire Department, Walla Walla County Fire District #4 and the College Place Fire Department responded to the fire.
After the fire was contained, firefighters responded to another reported fire in the 1800 block of Center Street., where they found minor damage to a home. They say that damage was caused by children playing with matches.