Lemhi Pass

Lemhi Pass
View from Lemhi Pass
Elevation	7,373 ft (2,247 m)
Traversed by	Unpaved road
Location	Lemhi County, Idaho/Beaverhead County, Montana, United States
Range	Bitterroot Rangeof theRocky Mountains
Coordinates	44°58′27″N113°26′42″W

Lemhi Pass
U.S. National Register of Historic Places
U.S. National Historic Landmark
Nearest city	Tendoy, Idaho
Coordinates	44°58′27″N113°26′42″W
NRHP referenceNo.	66000313
Significant dates
Added to NRHP	October 15, 1966
Designated NHL	October 9, 1960

Lemhi Passis a highmountain passin theBeaverhead Mountains,part of theBitterroot Rangein theRocky Mountainsand withinSalmon-Challis National Forest.The pass lies on theMontana-Idahoborder on theContinental Divide,at anelevationof 7,373 feet (2,247 m)above sea level.It is accessed via Lemhi Pass Road in Montana, and the Lewis and Clark Highway in Idaho, both gravel 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 theLemhi Shoshoneacquired horses and used the route to travel between the two main parts of their homeland.From the time of theLouisiana Purchasein 1803 until theOregon Treatyin 1846 the pass marked the western border of the United States. On August 12, 1805Meriwether Lewisand three other members of theLewis and Clark Expeditioncrossed 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 metCameahwaitand 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 theBlackfootpeople, so that in 1824Alexander Rossreferred to the route as the Blackfoot route.At that time the pass itself was known as North Pass, to distinguish it fromSouth Pass.The pass derives its present name fromFort Lemhi,founded in 1855 byMormonmissionaries who were the first non-Indians to establish a sustained relationship with theSalmon RiverIndian people.

During the mining era the pass was used by stagecoaches, but the route fell into disuse after 1910, when theGilmore and Pittsburgh Railroadwas built through the nearbyBannock Pass.Only a single track dirt road now crosses the pass.

The pass was designated aNational Historic Landmarkin 1960.

Mineral resources

The Lemhi Pass district has been found to host manylanthanideminerals and the richest deposit ofthoriumin the US. In a study of 31 samples taken from 21 different veins, the ratio ofrare-earth elements(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 asthoritehosted inquartzveins, whereas REEs are contained withinmonazite.

The deposits lie within quartz veins hosted inPrecambrianrock with minerals such ashematite,apatite,feldspar,thorite and monazite present. The monazite is found to be enriched in the middle rare earths, specificallyneodymium(Nd), as there is estimated to be 35 weight percent of Nd in the monazite.Neodymium,cerium,gadolinium,yttrium,anddysprosiumare the top lanthanide minerals recorded to be attainable in the Lemhi Pass.

See also

• Mountain passes in Montana
• List of National Historic Landmarks in Idaho
• List of National Historic Landmarks in Montana
• National Register of Historic Places listings in Lemhi County, Idaho
• National Register of Historic Places listings in Beaverhead County, Montana

External links

• National Park Service- Lemhi Pass
• Reading 2: Lemhi Pass and Lolo TrailfromThe Lewis & Clark Expedition: Documenting the Uncharted Northwest Name,a National Park Service Teaching with Historic Places (TwHP) lesson plan.
• National Register of Historic Places Registration: Lemhi Pass
• Accompanying 10 photos, from 1958 and 1962