A tributary of the Willamette River, which is joins just north of Albany, the Santiam rises in the central Oregon Cascades. One of its two main branches, the North Santiam, flows near Stayton and past North Santiam State Park. Still farther upstream is Detroit Dam, behind which is Detroit Lake and Detroit Lake State Park.
The South Santiam passes Lebanon and Sweet Home. The Middle Fork splits off behind Foster Dam, which forms Foster Lake, and is again dammed by Green Peter Dam, which forms Green Peter Lake. Both lakes are prime areas for recreation.
Cascadia State Park is located in the upper reaches of the South Santiam.