The McCash Fire was first seen on July 31 in the area of Ten Bear Mountain in the Marble Mountain Wilderness.
The lightning-sparked fire is actively burning in timber with an understory of tall grass and brush.
As of September 3, the fire was 51,297 acres in size and 6% contained.
An evacuation warning has been issued for the community of Happy Camp ad the surrounding area.
The northeast portion of the fire ran up against the Klamath River and Highway 96. Crews said they were able to keep the fire from crossing the river.
The Forest Service said there was no major growth on the southeast portion of the fire, but the east side of the fire will continue to grow.
Going forward, crews will focus on mop-up activities and building contingency lines as warm weather returns to the area.
For the latest updates about the McCash Fire, visit https://inciweb.nwcg.gov/incident/7757/