[7] The westernmost tributary is the Illinois River, which rises in southern Josephine County, in the Red Buttes Wilderness.

The river flows generally northwest along the west side of the Klamath Mountains, past Cave Junction and Kerby then through the Siskiyou National Forest.

It joins the Rogue River from the south on the Curry–Josephine county line, approximately 15 mi (24 km) from the Pacific Ocean.

The region is well suited for growing Burgundy varietals, similar to those grown in the Willamette Valley.

[6][7] Bear Creek is the most populated of the Rogue River tributaries, as it flows through the cities of Medford and Ashland.

[6] The climate of the Bear Creek Valley is similar to that of Bordeaux, and it is well suited for cultivating varietals such as Cabernet Sauvignon, Merlot, Chardonnay, Cabernet Franc, Pinot gris, Sauvignon blanc, Malbec and Syrah.