Pocatello — Area Geology

Pocatello — Area Geology. . , Portneuf Narrows , The Portneuf River cuts through a weak spot in the Bannock Range near a fault that formed 100 million years ago, during development of the Idaho – Wyoming thrust belt. Rocks north of the Narrows have been turned upside down by folding. , Scout Mountain , This mountain contains glacial deposits left by a huge ice sheet 700 million years ago. More recent block faulting uplifted these rocks thousands of feet. , Pocatello Valley and West Bench , The benches flanking the valley are alluvial fans eroded from the adjacent mountains. Steep faces on the benches were cut by the ancestral Portneuf River and were scoured clean by the Bonneville Flood. 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 , This craggy pile of rhyolite lava, forming the end of the ridge to the west, erupted from the Snake River Plain eight million years ago. , Red Hill , Just east of ISU, this hill is composed of sandstone and conglomerate, similar to formations high on Kinport Peak. , Chinks Peak , Beneath this peak are metamorphosed basaltic lavas, the oldest rocks in southeast Idaho, which erupted under waters 750 million years ago. , Sixth U.S. Army Command and General Staff College , First Class June 11-23, 1989, ISU.