The Highwood Mountains are an island range (sub-range of the Rockies entirely surrounded by prairie) which cover approximately 4,659 km² (1,799 sq mi) of the

Central Montana Alkalic Province The central Montana Alkalic Province is located in the United States in central Montana. Montana is bordered by Idaho, Wyoming, North Dakota, South Dakota, and Canada to the north. Central Montana is unique when compared to the rest of the Rocky M ...

in north central

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 ...

in the

U.S. 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 territori ...

They are in

Chouteau Chouteau was the name of a highly successful, ethnically French fur-trading family based in Saint Louis, Missouri, which they helped found. Their ancestors Chouteau and Laclède initially settled in New Orleans. They then moved-up the Mississipp ...

Judith Basin Judith Basin County is a county in the U.S. state of Montana. As of the 2020 census, the population was 2,023. Its county seat is the town of Stanford. History Judith Basin County was formed of area taken from western Fergus and eastern Casca ...

and

Cascade Cascade, Cascades or Cascading may refer to: Science and technology Science *Cascade waterfalls, or series of waterfalls * Cascade, the CRISPR-associated complex for antiviral defense (a protein complex) * Cascade (grape), a type of fruit * Bioc ...

counties and lie east of

Great Falls Great may refer to: Descriptions or measurements * Great, a relative measurement in physical space, see Size * Greatness, being divine, majestic, superior, majestic, or transcendent People * List of people known as "the Great" *Artel Great (born ...

and Benton Lake National Wildlife Refuge, at the northern end of the

Lewis and Clark National Forest Lewis and Clark National Forest is located in west central Montana, United States. Spanning , the forest is managed as two separate zones. The eastern sections, under the Jefferson Division, is a mixture of grass and shrublands dotted with "islan ...

. The mountains were included in

Highwood Mountains National Forest Highwood Mountains National Forest was established as the Highwood Mountains Forest Reserve by the U.S. Forest Service in Montana on April 12, 1906 with . It became a United States National Forest, National Forest on March 4, 1907. On July 1, 1908 ...

until 1908, when the unit became part of Lewis and Clark National Forest. Nearby are

Highwood, Montana Highwood is an unincorporated community and census-designated place (CDP) in Chouteau County, Montana, United States. The population was 176 at the 2010 census. History Highwood first had a post office in 1881, which closed and reopened a few ti ...

and the Missouri River above the mouth of the

Marias River The Marias River is a tributary of the Missouri River, approximately 210 mi (338 km) long, in the U.S. state of Montana. It is formed in Glacier County, in northwestern Montana, by the confluence of the Cut Bank Creek and the Two Medi ...

. The highest point in the Highwood Mountains is Highwood Baldy at 2338 meters (7670 ft). The area has

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

origins and is rich in

potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.

. Many of the

extrusive rock Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the Earth's atmosphere, atmosphere to fall back as Pyroclastic ...

s and some of the

dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

rocks contain abundant

phenocrysts 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

of a clear

analcime Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is Na Al Si2 O6· H2O. Minor amounts of potassium and calciu ...

that appears to be primary. Pseudoleucite is an abundant constituent of many of the

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock ...

s.''Potash Analcime and Pseudoleucite from the Highwood Mountains of Montana,'' Esper S. Larson and Bennett Frank Buie
/ref> The

Shonkin Sag The Shonkin Sag is a prehistoric fluvioglacial landform located along the northern edge of the Highwood Mountains in the state of Montana in the United States. The Sag is a river channel formed by the Missouri River and glacial meltwater pouring ...

, a glacial

meltwater channel A meltwater channel (or sometimes a glacial meltwater channel) is a channel cut into ice, bedrock or unconsolidated deposits by the flow of water derived from the melting of a glacier or ice-sheet. The channel may form on the surface of, within, b ...

, borders the Highwood Mountains to the north. Highwood Mountains Montana Southeast Face 17

Notes

Mountain ranges of Montana Geology of Montana Landforms of Chouteau County, Montana Lewis and Clark National Forest {{LewisandClarkCountyMT-geo-stub

See also

Notes