The Illinois River is a wild and scenic waterway that originates in the Siskiyou Mountains near the Oregon-California border. Flowing northward through the rugged Kalmiopsis Wilderness, it joins the Rogue River after a 56-mile journey. This remote river system drains a watershed of approximately 980 square miles. The Illinois offers some of the most challenging whitewater in Oregon, with difficulty ranging from Class II to V.

The 31-mile wilderness run from Miami Bar to Oak Flat is considered the premier multi-day trip, featuring over 150 rapids including the infamous Class V Green Wall. This section requires advanced whitewater skills and is typically run in 3-4 days. Upstream, the Highway 199 to Miami Bar stretch provides a mix of Class II-III rapids with some Class IV-V sections near McCaleb Ranch.

The best time to paddle the Illinois is typically late April to early May when water levels are reliable and days are longer. The river is known for its fickle nature, with flows that can fluctuate rapidly due to rainfall. The Illinois flows through a stunning canyon of serpentine and metamorphic rock, surrounded by diverse flora including Port Orford cedar, Jeffrey pine, and rare endemic plants adapted to the unique soil. Wildlife such as black bears, river otters, and ospreys can be spotted along the banks.

Key landmarks include the Class V Green Wall rapid at mile 18.1, Little Green Wall (Class IV+) at mile 18.8, and numerous scenic campsites like Pine Flat and Collier Creek. The main access points are Miami Bar (near Briggs Creek) for put-in and Oak Flat for take-out, with the nearest town being Selma, Oregon.

The river holds cultural significance for the Tolowa Dee-ni' Nation and was an important gold mining area in the late 19th century. Today, it's valued for its pristine wilderness character and challenging paddling opportunities.

Safety considerations include the river's remoteness, lack of cell service, and potential for rapidly changing conditions. A permit is required for floating the Wild and Scenic section. Multi-day trips should be well-prepared with proper equipment and experienced leadership due to the river's difficulty and isolation.