Red Rock Pass is a low

mountain pass A mountain pass is a navigable route through a mountain range or over a ridge. Since many of the world's mountain ranges have presented formidable barriers to travel, passes have played a key role in trade, war, and both Human migration, human a ...

in the

western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmania, a locality in Australia *Western world, countries that id ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

in southeastern

Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...

, located in southern Bannock County, south of

Downey Downey may refer to: People *Downey (surname) *Robert Downey Jr. Places *Downey, California, US *Downey, Idaho, US *Downey, Iowa, US Businesses *W. & D. Downey, photographic studio *Downey Studios, created out of a former Boeing plant Schools * ...

. It is geologically significant as the

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

of ancient

Lake Bonneville Lake Bonneville was the largest Late Pleistocene paleolake in the Great Basin of western North America. It was a pluvial lake that formed in response to an increase in precipitation and a decrease in evaporation as a result of cooler temperature ...

. It is traversed by

U.S. Route 91 U.S. Route 91 or U.S. Highway 91 (US-91) is a north–south United States highway running from Brigham City, Utah, to Idaho Falls, Idaho, in the U.S. states of Idaho and Utah. Despite the "1" as the last digit in the number, US-91 is no lon ...

at an

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

of above

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

, bounded by two mountain ranges; the Portneuf to the east and the

Bannock Bannock may mean: * Bannock (food), a kind of bread, cooked on a stone or griddle * Bannock (Indigenous American), various types of bread, usually prepared by pan-frying * Bannock people, a Native American people of what is now southeastern Oregon ...

to the west. The pass was cut through resistant

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

, and forms a narrow gap in length. At one time the pass was higher, where the shoreline of

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

Lake Bonneville stood. The pass takes its name from the red limestone cliffs which border it. Red Rock Pass has a surface deposit of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

silty

alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

with

topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...

of dark grayish brown silt

loam Loam (in geology and soil science) is soil composed mostly of sand (particle size > ), silt (particle size > ), and a smaller amount of clay (particle size < ). By weight, its mineral composition is about 40–40–20% concentration of sand–sil ...

Bonneville flood

It is believed that during the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

s in the vicinity of

Pocatello Pocatello () is the county seat of and largest city in Bannock County, with a small portion on the Fort Hall Indian Reservation in neighboring Power County, in the southeastern part of the U.S. state of Idaho. It is the principal city of the ...

began to divert the Bear River through

Lake Thatcher A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

and then into Lake Bonneville. This sudden influx caused Bonneville to overflow at Red Rock about 14,500 years ago. This overflow caused a sudden

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

of unconsolidated material on the northern shoreline near Red Rock Pass. As the material gave way, Marsh Creek Valley, immediately downstream, was flooded from wall to wall, and the rapid discharge eroded the pass to its present level. The flood then flowed into the

Snake River Plain image:Snake River view near Twin Falls, Idaho.jpg, The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature ...

, generally following the path of the present-day

Snake River The Snake River is a major river of the greater Pacific Northwest region in the United States. At long, it is the largest tributary of the Columbia River, in turn, the largest North American river that empties into the Pacific Ocean. The Snake ...

to its outlet in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...

.Univ. of Utah Media
– Lake Bonneville – accessed 2009-08-19 The Bonneville flood, as it is known, was a catastrophic event. The maximum discharge was about 15 million cubic feet per second (420,000 m³/s), or about three times the average flow of the

Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile. The headwaters of t ...

, the world's largest river. The speed of flow was approximately , and though peak flow lasted only a few days, voluminous discharges may have continued for at least a year.

References

External links

Huge Floods.com
– Bonneville

– Lake Bonneville {{Idaho Landforms of Bannock County, Idaho Historical geology Mountain passes of Idaho Geology of Idaho Natural history of Idaho