The Willow Fire was first reported on July 6 at a size of approximately 10 acres, according to the South Central Oregon Fire Management Partnership.
Multiple fire resources responded to burning grass and scattered juniper near the Willow Valley Reservoir.
Firefighters established a line around the fire in attempt to keep it contained to 346 acres.
On July 7, crews will continue to work to strengthen the perimeter.
69 fire personnel are at the scene of the Willow Fire.