U.S. Route 20 (US 20) is the portion of an east–west

U.S. Highway The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these h ...

in the state of

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 ...

. It begins northwest of

Parma Parma (; egl, Pärma, ) is a city in the northern Italian region of Emilia-Romagna known for its architecture, Giuseppe Verdi, music, art, prosciutto (ham), Parmigiano-Reggiano, cheese and surrounding countryside. With a population of 198,292 ...

at the Oregon state line and enters Montana away from the

Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowston ...

west entrance. Since 2019, US 20 has been designated as the Idaho Medal of Honor Highway.

Route description

At the western border, adjacent to

Nyssa, Oregon Nyssa is a city in Malheur County, Oregon, United States. The population was 3,267 at the 2010 census. The city is located along the Snake River on the Idaho border, in the region of far eastern Oregon known as the "Treasure Valley". It is pa ...

, US 20 ( running concurrently with US 26) crosses the

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 ...

into Idaho at an approximate

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 ...

. It joins US 95 and runs southbound to

. US 20/US 26 leaves US 95 southeast of Parma and runs to Caldwell, where it briefly joins Interstate 84 (I-84) (and US 30) from exit 26 until exit 29. These four highways parallel each other east (on two roadways) to

Boise Boise (, , ) is the capital and most populous city of the U.S. state of Idaho and is the county seat of Ada County. On the Boise River in southwestern Idaho, it is east of the Oregon border and north of the Nevada border. The downtown area' ...

where US 20/US 26 runs through downtown, then southbound on Broadway Avenue to rejoin with I-84/US 30 at exit 54. The four concurrent routes head southeast to Mountain Home, where US 20/US 26 departs at exit 95 to head east, past

Rattlesnake Station Rattlesnake Station was a stagecoach station northeast of Mountain Home, Idaho, and the original site of the Mountain Home post office. Approximately seven miles from exit 95 on Interstate 84 in present-day Elmore County, a historical marker l ...

Anderson Ranch Dam Anderson Ranch Dam is an earth rockfill type dam in the western United States, on the South Fork of the Boise River in southwestern Idaho. In Elmore County northeast of Mountain Home, it is several miles north of U.S. Route 20 ...

road, and crests at Cat Creek summit at . This portion of the route is near

Goodale's Cutoff Goodale's Cutoff formed a spur of the Oregon Trail beginning in Idaho, United States. The cutoff left the trail near Fort Hall, crossed the Snake River Plain to the Lost River, and then turned west to the area of Boise, crossing Camas Prairie. I ...

of the

Oregon Trail The Oregon Trail was a east–west, large-wheeled wagon route and Westward Expansion Trails, emigrant trail in the United States that connected the Missouri River to valleys in Oregon. The eastern part of the Oregon Trail spanned part of what ...

. US 20/US 26 continues east, into and across Camas County through Fairfield to Timmerman Junction, the intersection in Blaine County with State Highway 75 (SH-75), the northbound route to Sun Valley,

Galena Summit Galena Summit is a high mountain pass in the western United States in central Idaho, at an elevation of above sea level. The pass is located in the Boulder Mountains, in the northwest corner of Blaine County, within the Sawtooth National Recre ...

, and

Stanley Stanley may refer to: Arts and entertainment Film and television * ''Stanley'' (1972 film), an American horror film * ''Stanley'' (1984 film), an Australian comedy * ''Stanley'' (1999 film), an animated short * ''Stanley'' (1956 TV series) ...

. US 20/US 26 goes through Picabo and

Carey Carey may refer to: Names * Carey (given name), a given name * Carey (surname), a surname ** List of people with surname Carey Places Canada * Carey Group, British Columbia; in the Pacific * Carey Island (Nunavut) in James Bay United Kingdom * ...

, joins with US 93, and on to Craters of the Moon and

Arco ARCO ( ) is a brand of gasoline stations currently owned by Marathon Petroleum after BP sold its rights. BP commercializes the brand in Northern California, Oregon and Washington, while Marathon has rights for the rest of the United States an ...

, where US 93 splits off and turns north-northwest to climb the

Big Lost River The Big Lost River is a major river in the U.S. state of Idaho, about long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed May 4, 2011 Description The river starts in the Rocky Mountai ...

valley. US 20/US 26 continues on through the

Idaho National Laboratory Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...

, where the highways split just west of Atomic City; US 26 heads southeast to

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 ...

and US 20 to

Idaho Falls Idaho Falls (Shoshoni language, Shoshoni: Dembimbosaage) is a city in and the county seat of Bonneville County, Idaho, Bonneville County, Idaho, United States. It is the state's largest city outside the Boise metropolitan area. As of the 2020 Un ...

, where it turns north-northeast to pass near

Rexburg Rexburg is a city in Madison County, Idaho, United States. The population was 39,409 at the 2020 census. The city is the county seat of Madison County and its largest city. Rexburg is the principal city of the Rexburg, ID Micropolitan Statist ...

as a freeway. US 20 then climbs through the communities of St. Anthony, Ashton, and Island Park, and crosses 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 ...

Targhee Pass Targhee Pass is a mountain pass in the western United States on the Continental Divide. It is located along the border between southeastern Idaho and southwestern Montana, in the Henrys Lake Mountains at an elevation of above sea level. The ...

at , entering

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 ...

west of

West Yellowstone West Yellowstone is a town in Gallatin County, Montana, United States, adjacent to Yellowstone National Park. The population was 1,272 at the 2020 census. West Yellowstone is served by Yellowstone Airport. It is part of the Bozeman, MT Micropoli ...

History

US 20 was expanded past Yellowstone National Park in 1940, replacing the original US 191 and several state highways. Its original alignment through Boise included Main Street and Fairview Avenue for westbound and eastbound traffic, respectively, and Capitol Boulevard. US 20 and US 26 were realigned onto Myrtle and Front streets as well as Broadway following the completion of the Boise Connector extension on August 7, 1992. The Rigby Freeway section of US 20, extending from Idaho Falls to St. Anthony, was constructed in the 1970s. Its northernmost section still featured at-grade intersections until the 2000s, when they were replaced with full interchanges.

Junction list

References

External links