Yolla Bolly-Middle Eel Wilderness, Protected wilderness area in Mendocino County, United States.

Yolla Bolly–Middle Eel Wilderness spans 283 square miles across Mendocino, Tehama and Trinity counties, from 820 metres to Mount Linn's 2,466-metre summit. Its ridges hold headwaters of the Middle and North Forks of the Eel River, the Mad River and the South Fork Trinity River. Gray greenstone forms the northern peaks; sandstone and serpentine of the Franciscan formation lie to the south, with glacial cirque basins above 1,800 metres.

In 1927 Chief Forester William Greeley directed supervisors to study forest areas for a new "wilderness" classification; by 1929 the Middle Eel–Yolla Bolla Primitive Area was proposed, then the largest in northern California at 810 km2. It was reduced to 433.8 km2 in 1931. Federal wilderness protection came with the Wilderness Act of 1964, and the area was enlarged in 1984 and 2006.

The name combines Wintun words: Yo-la, snow-covered, and Bo-li, high peak, plus a reference to the Middle Fork of the Eel River. The Wintun peoples of the region gave the phrase. The wilderness lies northeast of Covelo, and its Wintun name is recalled in the range's peaks.

The area can be accessed through 15 trailheads surrounding the boundary, with entry points from the towns of Covelo, Ruth, and Corning. Visitors should prepare for varying conditions since elevation and terrain differ significantly across the region.

The Cedar Basin area holds the farthest western stand of quaking aspen trees, and the south side of Shell Mountain has a rare stand of junipers. Above roughly 6,000 feet (1,800 m), cirque basins left by former glaciers are visible.