Pocatello in Bannock County, Idaho — The American West (Mountains)
The Great Bonneville Flood
Photographed by Cosmos Mariner, July 8, 2024
1. The Great Bonneville Flood Marker
The marker is inscribed atop the concrete pedestal.
Prehistoric Lake Bonneville once filled much of the Great Basin. About 14,500 years ago, a natural gravel dam at Red Rock Pass gave way, and a flow five times the volume of the Amazon River rushed down Marsh Creek, through Portneuf Narrows and the present site of Pocatello, then on down the Snake and Columbia Rivers. Within a few months the lake was lowered more than 300 feet. The ancient shorelines from before and after the flood can be seen on the mountains near Salt Lake City and Ogden, Utah. The second largest flood known to have occurred on the earth, it scoured the basalt lava flow in Marsh Valley and at Pocatellos Ross Park. The lava was completely eroded from the Portneuf Narrows area. The flood-washed boulders in the Square were found during construction.
Erected 1989 by Leadership Pocatello, Greater Pocatello Chamber of Commerce, and the City of Pocatello.
Topics. This historical marker is listed in this topic list: Notable Events.
Location. 42° 51.669′ N, 112° 27.095′ W. Marker is in Pocatello, Idaho, in Bannock County. It can be reached from the intersection of South Arthur Avenue and Center Street, on the
this page online
Regionally, this marker is in Idaho’s Bear River Country. It is also in the American Mountain West. Globally, it is in North America, the Western Hemisphere, the Western World, and the Anglosphere.
Other nearby markers. At least 8 other markers are within walking distance of this marker: Volcanic Activity Near Pocatello (here, next to this marker); Simplot Square (a few steps from this marker); Nearby Historic Buildings (a few steps from this marker); Pocatello Area Geology (a few steps from this marker); American Indian Heritage (a few steps from this marker); The Bannock Hotel (a few steps from this marker); Railroad History (a few steps from this marker); Simplot (a few steps from this marker). Touch for a list and map of all markers in Pocatello.
Also see . . . Bonneville Flood (Wikipedia).
Excerpt: At the peak of the flood, approximately 33,000,000 cubic feet per second poured over the Snake River Plain at speeds of up to 70 miles per hour and deposited hundreds of square miles of sediments eroded from upstream. The flood scoured the 600-foot-deep Snake River Canyon through the underlying basalt and loess soil, creating Shoshone Falls and several other waterfalls along the Snake River. It also carved and increased in size many other tributary canyons, including those of the Bruneau River and Salmon Falls Creek.(Submitted on March 12, 2025, by Cosmos Mariner of Cape Canaveral, Florida.)The flood then entered Hells Canyon, significantly widening the gorge. Its waters eventually reached the Pacific Ocean via the Columbia River.Photographed by Cosmos Mariner, July 8, 20242. The Great Bonneville Flood MarkerLooking north through Simplot Park; South Arthur Avenue is on the right and Center Street crosses in the background.
Credits. This page was last revised on March 12, 2025. It was originally submitted on March 10, 2025, by Cosmos Mariner of Cape Canaveral, Florida. This page has been viewed 297 times since then and 46 times this year. Photos: 1, 2. submitted on March 12, 2025, by Cosmos Mariner of Cape Canaveral, Florida.
