Lemhi Pass is a high

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

Beaverhead Mountains The Beaverhead Mountains, highest point Scott Peak, el. , are a mountain range straddling the Continental Divide in the U.S. states of Montana and Idaho. (See also the GNIS link here.) They are a sub-range of the Bitterroot Range, and divide Be ...

, part of the

Bitterroot Range The Bitterroot Range is a mountain range and a subrange of the Rocky Mountains that runs along the border of Montana and Idaho in the northwestern United States. The range spans an area of and is named after the bitterroot (''Lewisia rediviva' ...

in the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

and within Salmon-Challis National Forest. The pass lies on the

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

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 ...

border on the

continental divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

, 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 ...

above sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The comb ...

. It is accessed via Lemhi Pass Road in Montana, and the Lewis and Clark Highway in Idaho, both dirt roads. Warm Springs Road, which roughly follows the divide in Montana, passes just west of the pass's high point.

History

The pass gained importance in the 18th century, when the

Lemhi Shoshone The Lemhi Shoshone are a tribe of Northern Shoshone, also called the Akaitikka, Agaidika, or "Eaters of Salmon".Murphy and Murphy, 306 The name "Lemhi" comes from Fort Lemhi, a Mormon mission to this group. They traditionally lived in the Lemhi Ri ...

acquired horses and used the route to travel between the two main parts of their homeland.Idaho State Historical Society Reference Series No. 280
From the time of the

Louisiana Purchase The Louisiana Purchase (french: Vente de la Louisiane, translation=Sale of Louisiana) was the acquisition of the territory of Louisiana by the United States from the French First Republic in 1803. In return for fifteen million dollars, or app ...

in 1803 until the

Oregon Treaty The Oregon Treaty is a treaty between the United Kingdom and the United States that was signed on June 15, 1846, in Washington, D.C. The treaty brought an end to the Oregon boundary dispute by settling competing American and British claims to t ...

in 1846 the pass marked the western border of the United States. On August 12, 1805

Meriwether Lewis Meriwether Lewis (August 18, 1774 – October 11, 1809) was an American explorer, soldier, politician, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition, also known as the Corps of Discovery, with ...

and three other members of the

Lewis and Clark Expedition The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the United States expedition to cross the newly acquired western portion of the country after the Louisiana Purchase. The Corps of Discovery was a select gro ...

crossed the Continental Divide at Lemhi Pass. Lewis found a "large and plain Indian road" over the pass. This was the first time that white men had seen present-day Idaho:

We proceeded to the top of the dividing ridge from which I discovered immense ranges of high mountains still to the West of us with their tops partially covered in snow

The next day Lewis met

Cameahwait Cameahwait was the brother of Sacagawea, and a Shoshone chief. He was the head of the first group of inhabitants of modern-day Idaho who were encountered by Europeans. Cameahwait met Meriwether Lewis and three other members of the Lewis and Cla ...

and his band of Shoshone, and returned with them across the pass to meet Clark. On August 26, 1805 the entire expedition crossed the pass. In the early 19th century the pass was regularly used by the

Blackfoot The Blackfoot Confederacy, ''Niitsitapi'' or ''Siksikaitsitapi'' (ᖹᐟᒧᐧᒣᑯ, meaning "the people" or " Blackfoot-speaking real people"), is a historic collective name for linguistically related groups that make up the Blackfoot or Bla ...

people, so that in 1824 Alexander Ross referred to the route as the Blackfoot route. At that time the pass itself was known as North Pass, to distinguish from South Pass. The pass derives its present name from

Fort Lemhi Fort Lemhi was a mission approximately two miles (3 km) north of present-day Tendoy, Idaho, occupied by Mormon missionaries from 1855 to 1858. Approximately twenty-seven Mormon men left the Salt Lake Valley on May 18, 1855, as instructed by B ...

, founded in 1855 by

Mormon Mormons are a religious and cultural group related to Mormonism, the principal branch of the Latter Day Saint movement started by Joseph Smith in upstate New York during the 1820s. After Smith's death in 1844, the movement split into several ...

missionaries who were the first non-Indians to establish a sustained relationship with the Salmon River Indian people. During the mining era the pass was used by stagecoaches, but the route fell into disuse after 1910, when the

Gilmore and Pittsburgh Railroad The Gilmore and Pittsburgh Railroad (G&P), now defunct, was an American railroad located in southwestern Montana and east-central Idaho. Constructed in 1909 and 1910 between Armstead, Montana, and Salmon, Idaho, the G&P served mining and agricult ...

was built through the nearby

Bannock Pass Bannock Pass is a high mountain pass in the Beaverhead Mountains, part of the Bitterroot Range in the Rocky Mountains. The pass lies on the Montana-Idaho border on the Continental Divide, at an elevation of above sea level. The pass is crosse ...

. Only a single track dirt road now crosses the pass. The pass was designated a

National Historic Landmark A National Historic Landmark (NHL) is a building, district, object, site, or structure that is officially recognized by the United States government for its outstanding historical significance. Only some 2,500 (~3%) of over 90,000 places listed ...

in 1960.

Mineral resources

The Lemhi Pass district has been found to host many

lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...

minerals and the richest deposit of

thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...

in the US. In a study of 31 samples taken from 21 different veins, the ratio of

rare-earth elements The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...

(REEs) in the area is estimated to be between 0.05-9.2%. This depends largely on the localized mineralogy and REE mineralization. Most commonly the thorium is found as

thorite Thorite, (Th,U)SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to ...

hosted in

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

veins, whereas REEs are contained within

monazite Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the cerium- ...

.''Occurrence and Distribution of Rare Earths in the Lemhi Pass Thorium Veins, Idaho and Montana'' Mortimer H. Staatz, Van E. Shaw, and James S. Wahlberg (1972)
/ref> The deposits lie within quartz veins hosted in

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

rock with minerals such as

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...

, thorite and monazite present. The monazite is found to be enriched in the middle rare earths, specifically

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...

(Nd), as there is estimated to be 35 weight percent of Nd in the monazite."Rare Earth Elements and Other Critical Metals in Idaho, Geo Note, Idaho Geological Survey, Virginia S. Gillerman, January 2011
/ref> Neodymium,

cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...

gadolinium Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen ...

yttrium Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in com ...

, and

dysprosium Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...

are the top lanthanide minerals recorded to be attainable in the Lemhi Pass.

References

External links

National Park Service
- Lemhi Pass

from ''The Lewis & Clark Expedition: Documenting the Uncharted Northwest Name,'' a National Park Service Teaching with Historic Places (TwHP) lesson plan. * * {{Montana Mountain passes of Idaho Mountain passes of Montana National Historic Landmarks in Idaho National Historic Landmarks in Montana Great Divide of North America Landforms of Lemhi County, Idaho Landforms of Beaverhead County, Montana Borders of Idaho Borders of Montana Transportation in Lemhi County, Idaho Transportation in Beaverhead County, Montana Beaverhead-Deerlodge National Forest Salmon-Challis National Forest Natural features on the National Register of Historic Places in Montana National Register of Historic Places in Lemhi County, Idaho National Register of Historic Places in Beaverhead County, Montana Lewis and Clark Expedition