Confluence of the Clark Fork and Blackfoot Rivers The BonnerMilltownHistory,org website explores and celebrates the area around the confluence of the Clark Fork and Blackfoot Rivers. The area is flanked by mountain ranges and peaks: Bonner Mountain, in the Garnet Range, towers above its namesake community and Piltzville; across the Blackfoot River to the west, Woody Mountain of the Rattlesnake Range rises above West Riverside and Pine Grove; and across the Clark Fork to the south is Mount Sentinel and University Mountain, part of the Sapphire Range.