Copper Mines in the Pocatello Formation
The bedrock in Portneuf Narrows is ancient volcanic rock of the Bannock
Volcanic Member for the Pocatello Formation. Other unique rock in this area
records a continent-scale glaciation about 700 million years ago. After opening
of the Fort Hall Indian Reservation to settlement in 1902 a copper mine was
located in Fort Hall Mine Canyon directly south. A railroad siding and bunkhouse
served the area. A vein of chacopyrite copper ore was mined for several years but
the vein was cut off by a cross-fault, and despite 400 feet of tunnel under the mountain, it was never located again.