The Oak Grove Fork Clackamas River arises at an elevation of above sea level and falls between source and mouth to an elevation of . The main stem begins in the Cascade Range near Abbot Pass, a mountain gap at , on the border between Clackamas County and Wasco County. Originating on the Warm Springs Indian Reservation, the river flows generally west about through the Mount Hood National Forest to the unincorporated community of Ripplebrook, where it joins the main stem of the Clackamas River.