[3] The South Fork rises as a small stream draining out of Eden Valley, 2.5 miles (4.0 km) northwest of Mount Bolivar in the Siskiyou National Forest.

Picking up scores of tributaries, such as Wooden Rock, Clear and Panther Creeks, the river gains volume as it flows southwest into a deep gorge.

Now a fairly large stream, the South Fork winds through canyons to the confluence with Coal Creek before entering an alluvial valley near the small community of Powers.

About a mile downstream, Dement Creek enters from the left and the terrain around the river transforms from hills to farmland.

Anadromous fish including salmon and steelhead inhabit much of the river, but some habitat has been compromised due to poor watershed management practices such as excessive logging and clearing.