The North Fork of the river rises in the mountains of south central Skagit County and flows south into Snohomish County, then west to join the South Fork near Arlington. The South Fork rises near Big Four Mountain in east central Snohomish County and flows west and northwest to the North Fork. The combined river heads west to Port Susan and Skagit Bay at Stanwood. The river valley is at the end of the river’s run out to Skagit Bay and was an important farming center. Notable Washington Heritage Barns along the route include the Jensen Barn, Grimm Barn, Gerritzen Barn.