Entry in progress—B.P.
 
Wikipedia: Idaho
Idaho is a state in the northwestern region of the United States. Idaho is the 14th largest, the 39th most populous, and the 7th least densely populated of the 50 United States. The state’s largest city and capital is Boise. Residents are called “Idahoans”. Idaho was admitted to the Union on July 3, 1890, as the 43rd state.
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Idaho’s nickname is the “Gem State”, because nearly every known type of gemstone has been found there. In addition, Idaho is one of only two places in the world where star garnets can be found in any significant quantities, the other being India.
 
Etymology
The exact origin of the name remains a mystery. In the early 1860s, when the United States Congress was considering organizing a new territory in the Rocky Mountains, eccentric lobbyist George M. Willing suggested the name “Idaho”, which he claimed was derived from a Shoshone language term meaning “the sun comes from the mountains” or “gem of the mountains”. Willing later claimed that he had simply invented the name. Congress ultimately decided to name the area Colorado Territory when it was created in February 1861. Thinking they would get a jump on the name, locals named a community in Colorado “Idaho Springs”.
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Despite this lack of evidence for the origin of the name, many textbooks well into the 20th century repeated as fact Willing’s account that the name “Idaho” derived from the Shoshone term “ee-da-how”.
 
The name “Idaho” may be derived from the Plains Apache word “ídaahę́” which means “enemy.” The Comanches used this word to refer to the Idaho Territory.
 
Chronicling America
24 March 1860, New York (NY) Herald, “Territorial Affairs,” pg. 7, col. 2:
There seems to be considerable difficulty about selecting a name for the Pike’s Peak Territory. It has been called Jefferson; but those in authority assert that as there cannot be States enough to name after all of the Presidents, that it will not be policy to go beyond Washington, who stands “alone in his glory.” Acting upon this decision, the Senate Committee have before them the following names: “Tampa,” interpreted Bear; “Idahoe,” meaning Gem of the Mountains, “Nemara;” “Colorado;” “San Juan;” “Lulla,” interpreted Mountain Fairy; “Weapollah;” and “Arrapahoe,” the name of the Indian tribe inhabiting the Pike’s Peak region. The House COmmittee seem to have hit upon the very appropriate name of “Tahosa,” which means Dwellers of the Mountain Tops. This, or “Idahoe,” will probably be adopted.
   
1 May 1860, New York (NY) Herald, “News from Washington,” pg. 6, col. 6:
Idaho, “the Gem of the Mountains,” is adopted as the name of the Pike’s Peak Territory.
 
OCLC WorldCat record
Rocky Mountains gold mines : Idaho (gem of the mountains) Gold and Silver Mining Company, Quartz Hill, Nevada district, Pikes Peak.
Author: Geo M Willing; John W Woods
Publisher: Baltimore : John W. Woods, steam printer, No. 202 Baltimore Street, [1860]
Edition/Format:   Print book : English
 
19 March 1863, Christian Advocate and Journal, “Domestic Miscellany,” pg. 95,col. 1:
TERRITORY OF IDAHO.—Congress has passed a bill to make a new territory out of Eastern Oregon and Western Dakota, under the name of Idaho, which is Indian for Gem of the Mountains.
 
7 April 1866, The Daily Cleveland Herald (Cleveland, OH), “Geographical Nicknames,” pg. 2, col. 2:
...Idaho, Gem of the Mountains; ...
   
July 1867, Hours at Home; A Popular Monthly of Instruction and Recreation, pg. 272, col. 1:
FROM IDAHO TO SAN FRANCISCO.
THERE is a region far inland from the great Western Ocean, composed of deserts and mountains, with here and there an oasis of valley, like a green thread among the wastes, that bears the name of Idaho. he word, translated from the aboriginal, signifies “The Gem of the Mountains,” and the treasures of that territory, as developed of late and promised for the future, are proof that the region is aptly named.
 
OCLC WorldCat record
Idaho at the Columbian Exposition : gem of the mountains.
Publisher: [Boise?] : [publisher not identified], [1893]
Edition/Format:   Print book : English
 
OCLC WorldCat record
The Gem State rural.
Author: Gem State Rural Publishing Company.
Publisher: Caldwell, Idaho : [Gem State Rural Pub. Co.], 1895-1916.
Edition/Format:   Journal, magazine : Periodical : English
 
OCLC WorldCat record
The Gem state rural and the Idaho farmer.
Publisher: Spokane, Wash. ; Boise, Idaho : s.n., 1916-1920.
Edition/Format:   Newspaper : English
 
OCLC WorldCat record
Coeur d’Alene : the gem city of the gem state, Idaho.
Author: Coeur d’Alene Area Chamber of Commerce.
Publisher: [Coeur d’Alene, Id.] : [Coeur d’Alene Chamber of Commerce], [1934?]
Edition/Format:   Print book : English
     
Google Books
Focus on American English & Culture
By Pierfranca Forchini
Milan: EDUCatt - Ente per il diritto allo studio universitario dell’Università Cattolica
2014
Pg. 43:
Idaho
The name of the state is often (but incorrectly) supposed to be Indian for “gem of the mountains”. This has led the state to be nicknamed Gem of the Mountains, or most succinctly in more recent times, The Gem State.
 
OCLC WorldCat record
Idaho’s place : a new history of the Gem State
Author: Adam M Sowards; University of Idaho. Program in Pacific Northwest Studies.
Publisher: Seattle, WA : University of Washington Press, [2014]
Edition/Format:   eBook : Document : Biography : EnglishView all editions and formats
Database: WorldCat
Summary:
Focuses on Gem State history. From the state’s indigenous roots and early environmental battles to recent political and social events, this title includes essays that provided context for understanding Idaho’s important role in the development of the American West.