Near Pocatello, the Portneuf River cuts through a weak spot in the Bannock Range at Portneuf Narrows near a fault formed 100 million years ago during development of the Idaho-Wyoming thrust belt, and rocks north of the Narrows were turned upside down by folding. Scout Mountain contains glacial deposits left by a huge ice sheet 700 million years ago, and more recent block faulting uplifted these rocks thousands of feet. In Pocatello Valley and on West Bench, the valley-flanking benches are alluvial fans eroded from adjacent mountains, their steep faces were cut by the ancestral Portneuf River and scoured clean by the Bonneville Flood, and flood boulders and gravel cover the valley floor. Kinport Peak, the highest point on the ridge to the southwest, is underlain by quartzite and shale laid down under a shallow sea 650 million years ago. Howard Mountain, the craggy end of the ridge to the west, is made of rhyolite lava that erupted from the Snake River Plain eight million years ago. Red Hill, just east of ISU, is composed of sandstone and conglomerate similar to formations high on Kinport Peak. Beneath Chinks Peak are metamorphosed basaltic lavas, the oldest rocks in southeast Idaho, which erupted under waters 750 million years ago.