The fire reported at 1:05 p.m. and was controlled at 2:22 p.m., the dispatcher said.
The barn was used for storage and as an artist's typographical design studio, a dispatcher said.
Firefighters from Sonoma and the Schell-Vista Fire Protection District have responded and are receiving mutual aid from Glen Ellen and Kenwood, the dispatcher said.
There also might have been be a recreation vehicle in or near the burning structure, the dispatcher said.
No injuries have been reported.