At about from the mouth, the river receives Hackett Creek from the right, passes the unincorporated community of Brightwood shortly thereafter, and receives North Boulder Creek from the right. Barlow Trail County Park and remnants of the Barlow Road lie to the right along this stretch of the river. Between and from the mouth, the Salmon River enters from the left. Roughly later, Wildcat Creek enters from the left and then Alder Creek and Whiskey Creek, also from the left. The river passes the Marmot gauging station operated by the United States Geological Survey (USGS) in cooperation with Portland General Electric at river mile (RM) 29.8 (river kilometer (RK) 48.0). The unincorporated community of Marmot lies to the right of the river on a ridge—the Devil's Backbone—separating the Sandy River from the Little Sandy River to the north.