Officials said it was started by a lightning strike off Scales Ranch Rd.
The fire had burned around 322 acres within about 24 hours, according to TFS.
There is no immediate threat to homes or property and no roads have been closed, but TFS urges drivers to use caution in the area.
TFS officials said they are also working a five-acre grass fire near Atascocita. That fire started around 1:45pm Saturday.
