It flows north through the mountains past Marion Forks, receiving the drainage from the western slope of Mount Jefferson. Near Mount Jefferson it turns sharply west, descending through a canyon past Idanha and Detroit to Niagara County Park where the valley begins to widen and some agriculture use begins. Continuing west, the river flows past Gates, Mill City and Mehama. It emerges through the foothills into the Willamette Valley near Stayton, then flows 15 miles (24 km) southwest through the valley where it joins the South Santiam River to form the Santiam River. The confluence is approximately 10 miles (16 km) east of the confluence of the Santiam and the Willamette River.