There are four officially designated wilderness areas in Klamath National Forest that are part of the National Wilderness Preservation System.
Two of them extend into neighboring national forests, and one of those into land managed by the Bureau of Land Management.

Marble Mountain Wilderness
Russian Wilderness
Red Buttes Wilderness
Siskiyou Wilderness (mostly in Six Rivers NF)
Trinity Alps Wilderness (mostly in Trinity NF; partly in Shasta NF, Six Rivers NF, and BLM land)
There are four officially designated wilderness areas in Klamath National Forest that are part of the National Wilderness Preservation System. Two of them extend into neighboring national forests, and one of those into land managed by the Bureau of Land Management.
Marble Mountain Wilderness
Russian Wilderness
Red Buttes Wilderness
Siskiyou Wilderness (mostly in Six Rivers NF)
Trinity Alps Wilderness (mostly in Trinity NF; partly in Shasta NF, Six Rivers NF, and BLM land)
Klamath National Forest