South Fork Eel River Wilderness, Nature reserve in Mendocino County, United States.

South Fork Eel River Wilderness is a nature reserve in Mendocino County featuring rolling terrain with river valleys and mountain ridges. The landscape is dominated by forests that descend toward the waterway cutting through the area.

Congress added the South Fork Eel River Wilderness to the National Wilderness Preservation System in 2006 through the Northern California Coastal Wild Heritage Wilderness Act (Public Law 109-362). The Bureau of Land Management, part of the Department of the Interior, was put in charge of its 12,868 acres in Mendocino County.

Much of both units is designated a Research Natural Area and Area of Critical Environmental Concern, managed by the Bureau of Land Management. Elder Creek, in the Cahto Peak unit, is so unaltered that it holds Biosphere Reserve, National Natural Landmark and Hydrologic Benchmark status. The rare plants isolated on serpentine rock near Red Mountain's summit are the subject of this protection.

Access is mainly through hiking trails and rough forest roads reached from nearby communities. Visitors should be prepared for unpaved paths and varying terrain conditions.

The soil in the reserve has an unusual reddish color that supports rare plant species like Sargent cypress trees. These special conditions allow plants to thrive that are difficult to find elsewhere.