The South Fork Salmon River is a river in Siskiyou County, California and is the larger of two tributaries that join to form the Salmon River, the other being the North Fork. It begins in the Salmon Mountains, on the border of Siskiyou and Trinity County, about southeast of Cecilville, and flows generally northwest through the Salmon Mountains to its confluence with the North Fork at Forks of Salmon. The South Fork drains an area of , located entirely in the Klamath National Forest, with a significant portion in the Trinity Alps Wilderness.