About Bannock County
Bannock County was established March 6, 1893, covering 1,113 square miles in southeastern Idaho with the county seat at Pocatello. It was named after the Bannock Indians who inhabited this area. The 2000 census shows 75,565 people living here, with some 60,000 of them in the Pocatello area.
Fort Hall was the first white settlement in Bannock County, built by 1834 by Nathaniel Wyeth. This became an important trading post on the Oregon Trail. When the railroad was extended through this area, Pocatello, situated at a junction, became an important city.
Bannock County is centered around the Portneuf River which enters the county from the east and then flows northward into the Snake River close to the northern border of the county. The Snake River Basin is a vast plain which covers much of Idaho, but only the northernmost sliver of Bannock County. The rest of the county is covered by mountains interspersed by valleys.
Bannock County has a bit of interesting geologic history. A vast inland sea, called Lake Bonneville, at one time covered much of Utah and extended into Idaho just about to the southern boundary of the county. The Bear River, which used to flow into the Portneuf River, was diverted into Lake Bonneville by a lava flow, which led to the lake overflowing its banks and discharging a flood into Marsh Valley which for a time was probably several times the size of the Amazon River. This torrent flowed through the length of the county from south to north, into the Snake River, and out into the Pacific Ocean. The remnant of Lake Bonneville is now known as Great Salt lake.
Interstate 15 is the main route through Bannock County, heading north-south through Marsh Valley and Pocatello. U.S. Highway 30 goes east-west through the county, but joins the freeway at McCammon instead of crossing the mountains which block the route to the west. U.S. Highway 91 mostly follows the freeway, but diverges through Pocatello, and on the south end, leaves the freeway at the town Virginia to go further east into Cache Valley.