The South Santiam River is a tributary of the Santiam River, about long, in western Oregon in the United States. It drains an area of the Cascade Range into the Willamette Valley east of Corvallis. It rises in the Cascades in southeastern Linn County in the Willamette National Forest at . From this source, the confluence of Sevenmile and Squaw creeks, it flows briefly north, then generally west through the Western Cascades and Cascadia. It then flows a handful of miles before entering Foster Reservoir. At Foster Reservoir the Middle Santiam River joins the South Santiam. Downstream from the reservoir it flows west past Sweet Home, where it turns northwest, passing through the foothills into the Willamette Valley near Lebanon. It joins the North Santiam River from the southeast to form the Santiam approximately northeast of Lebanon, about east of the confluence of the Santiam with the Willamette River. U.S. Route 20 follows the valley of the river from near its headwaters in the mountains to the Willamette Valley northwest of Lebanon. Tributaries Named tributaries from source to mouth are Sevenmile and Squaw creeks at the headwaters, then Three, Sheep, Elk, Soda Fork, Stewart, and Keith creeks. Then come Boulder, Little Boulder, Trout, Falls, Moose, Canyon, and Wolfe creeks. Further downstream are Dobbin, Soda, Cabin, Bucksnort, Mouse, and Deer creeks. Below those are Shot Pouch Creek and the Middle Santiam River. Then come Ralston, Gadney, Wiley, Ames, Roaring, McDowell, Hamilton, and Onehorse creeks followed by Spring Branch. Entering the lower reaches of the river are Crabtree, Thomas, and Mill creeks, and the North Santiam River. See also List of longest streams of Oregon List of rivers of Oregon Willamette Riverkeeper References External links North Santiam Watershed Council South Santiam Watershed Council Willamette Riverkeeper Rivers of Oregon Rivers of Linn County, Oregon