In 1927 U.S. Chief Forester William Greeley directed the district supervisors to study and recommend areas in the nation's forests suitable for a new classification as "wilderness". By 1929 fourteen areas in the California Region 5 forests were proposed for this designation. The regulations for wilderness areas, known as the L-20, became − with modifications by Secretary of AgricultureWilliam Jardine − the management policy for these areas. The L-20 Regulations used the term "primitive areas" with the purpose stated as to:
Of the three new "primitive areas" located in northern California, the Middle Eel–Yolla Bolla Primitive Area was the largest at. The size was reduced to in 1931. By the close of 1932 California had eighteen new primitive areas protecting. Federal protection was given when this area became part of the National Wilderness Preservation System, created by the passage of the Wilderness Act of 1964.
Waterways
Located within the southern Klamath Mountains and Inner NorthernCalifornia Coast Ranges, the rugged topography of the Yolla Bolly–Middle Eel Wilderness protects headwaters of the Middle Fork of the Eel River, the North Fork of the Eel, the Mad River, and the South Fork of the Trinity River. The eastern side has the watersheds of Cottonwood and Thomes Creeks, which flow into the Sacramento River. The very northern tip of the wilderness—around the summits of Black Rock Mountain and North Yolla Bolly Peak—are in the Klamath Mountains. Both the Middle and North Forks of the Eel River have Wild and Scenic River designation, as does the South Fork of the Trinity River. Several small, shallow lakes occur in remnant glacial basins near the highest peaks. Numerous springs are found off of the main ridgetops.
Flora and fauna
The wilderness has Coast Range and Klamath montane, mixed evergreen and Douglas fir forest types. Conifers include the California endemic foxtail pine, ponderosa pine, red and white firs, western white pine, sugar pine, incense cedar, and the rare Pacific yew. Other tree species include oaks and cottonwoods. The area includes wet meadows and open grasslands supporting abundant deer herds. Lower elevations have chamise, manzanita, and ceanothus. Wildlife in the wilderness includes black bear, Roosevelt Elk, black-tailed deer, gray fox, mountain lion, bobcat, coyote, northern flying squirrel, fisher and martin. The northern spotted owl can be found here, as well as eagles, hawks, turkey vultures and smaller birds like grouse, quail, and bandtailed pigeon. Rainbow trout live in most larger streams, such as in the South Fork of Cottonwood Creek, and in Black Rock Lake. The Middle Fork Eel River watershed has summer- and winter-run steelhead and spring-run chinook salmon, but fishing is restricted.
Geology
Rocks in the northern mountains are predominantly gray greenstone while the southern mountains include sandstone and serpentine of the Franciscan formation. Cirque basins from former glaciers are seen above about elevation. Extensive faulting in the rocks makes the region prone to erosion, slumping and landslides. One modern landslide near Ides Cove, on the north flank of Mount Linn, reached more than two miles toward the South Fork Cottonwood Creek, upending old-growth forests and leaving large fissures on its perimeter.
Recreation
Recreational activities include backpacking, day-hiking, camping, fishing hunting, and nature photography. There are 15 trailheads all around the wilderness boundary with the most frequent users being hunters in the autumn months. Visitor use has one of the lowest densities among wilderness areas in California. The Ides Cove Loop Trail is over in length and travels through very scenic areas. This trailhead is also the beginning of the Bigfoot Trail. The US Forest Service encourages visitors to use Leave No Trace ethics when visiting the wilderness to minimize impact to the environment. Access to trailheads on the northwest side of the wilderness is available by paved road from Ruth. Other roads suitable for most passenger vehicles reach the south boundary from Covelo and the east boundary from Corning or Red Bluff.