Course
It rises in the high Cascades north of Fish Mountain, formed by the confluence of two short forks in eastern Douglas County approximately 20 miles (32 km) northwest of Crater Lake. It flows generally southwest through a remote canyon in the Umpqua National Forest to Tiller, then west past Milo and Days Creek. It emerges into the South Umpqua Valley at Canyonville, passing under Interstate 5 and flowing north along highway past Tri-City, Myrtle Creek, and Roseburg. It joins the North Umpqua from the south to form the Umpqua approximately 6 miles (10 km) northwest of Roseburg.
It receives Cow Creek from the south approximately 5 miles (8 km) southwest of Tri-City.
One of the main tributaries of the South Umpqua River is Cow Creek, which also flows west from the Cascade Mountains, but South of Canyonville. On its westward journey, the Cow Creek more or less runs parallel to the South Umpqua River, with an East-West mountain ridge separating them.
Cow Creek runs further west, swings around north and makes its confluence with the South Umpqua River at Tri City. The Cow Creek has such a significant flow that it is almost a toss-up as to which should be called the river and which the creek.
Read more about this topic: South Umpqua River