Intermountain West
The Intermountain West, also known as the Intermountain Region, is a distinct geographic and geological area located within the Western United States. This expansive region is defined by its position between two major mountain systems: the Rocky Mountain Front to the east and the Cascade Range and Sierra Nevada to the west.
Spanning multiple states, the region is characterized by its unique topography and a diverse array of ecosystems that range from arid deserts to high-altitude coniferous forests.
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Key Facts
- Location: Situated between the Rocky Mountains, Sierra Nevada, and Cascade Range.
- Topography: Defined by a mix of basin and range landscapes and high plateaus.
- Hydrology: Features both ocean-reaching rivers (Columbia and Colorado) and endorheic basins (internal drainage).
- Climate: Heavily influenced by rain shadows, resulting in generally arid conditions with hot summers.
- Culture: Historically home to numerous Native American tribes and later the center of the Mormon Corridor.
Topography and Hydrology
The landscape of the Intermountain West is primarily composed of basin and range and plateau topography. This geological structure creates a series of alternating mountain ranges and flat valleys.
Water systems in the region vary significantly. Major rivers, such as the Colorado River and the Columbia River, successfully flow to the Pacific Ocean. In contrast, other streams—including the Owens River and the Walker River—are located in endorheic basins (drainage basins that do not connect to any ocean). These waters typically flow into desert sinks or lakes that are either seasonally dry or brackish.
The region is divided into several key geological portions:
- Basin and Range Province
- Colorado Plateau
- Great Basin
- Intermontane Plateaus
Climate Patterns
Climate in the Intermountain Region is dictated by elevation and geographic positioning. Much of the area sits in the rain shadow of the Cascade and Sierra Nevada ranges, which block moisture-bearing storms from the Pacific Ocean, leading to drier conditions.
Seasonal weather varies by latitude. The northern reaches experience cold, moist winters, while the southern portions see shorter, warmer winters with less snowfall. Regardless of latitude, the region is characterized by hot summers. Additionally, the mid-summer months may bring North American Monsoon storms, which travel northeast from the Mexican Plateau and the Pacific Ocean.
Natural History and Ecology
The biological diversity of the Intermountain West is closely tied to elevation. Lower elevations are dominated by xeric shrublands (plants adapted to dry conditions), deserts, and temperate grasslands. As elevation increases, the environment shifts to montane habitats featuring temperate coniferous forests. These forests consist of various species of cedar, pine, juniper, and aspen, supported by perennials and understory shrubs.
The region's diverse ecoregions include:
- Forests: North Central and South Central Rockies, Colorado Rockies, Arizona Mountains, and the Wasatch and Uinta montane forests.
- Grasslands and Shrublands: The Columbia Plateau, Palouse grasslands, Montana Valley and Foothill grasslands, and the Colorado Plateau Shrublands.
- Deserts: The Snake River Plain, Central Basin and Range, Northern Basin and Range, and the Great Basin shrub steppe.
Human interaction with the land includes cattle ranching and agriculture. Through the use of water diversions for irrigation, farmers cultivate crops such as alfalfa, grass hay, sugar beets, potatoes, and corn, with the former two primarily serving as livestock feed.
Demographics and Sociology
For millennia, the Intermountain West served as the homeland for various Native American bands, tribes, and cultures. The region underwent significant cultural shifts starting in the 18th century with the northern fur trade and continuing through the 19th-century westward expansion of the United States.
The development of the first transcontinental railroad further accelerated the settlement of non-native populations. A notable sociological feature of the region is the Mormon Corridor, centered in Utah, which maintains the highest percentage of Latter-day Saint (LDS) members in the United States.
Regional Scope
The Intermountain states are generally classified as part of the Mountain States. The region encompasses all or parts of the following areas:
| State | Included Area |
|---|---|
| Nevada, Utah, Idaho | Entire State |
| Montana | Western third |
| Arizona | North of the Mogollon Rim |
| Colorado | Front Range westward |
| New Mexico | Central mountain chain westward |
| California | East of the Sierra Nevada Mountains |
| Oregon, Washington | East of the Cascade Mountains |
| Texas | Far West, from the Pecos River westward |
Frequently Asked Questions
What defines the boundaries of the Intermountain West?
The region is bounded by the Rocky Mountain Front to the east and the Sierra Nevada and Cascade Range to the west.
What is an endorheic basin?
An endorheic basin is a drainage area where the rivers and streams do not reach the ocean, instead flowing into internal lakes or desert sinks.
How does the rain shadow effect impact the region?
The Cascade and Sierra Nevada ranges block precipitation from Pacific storms, creating a rain shadow that results in the arid climates found throughout much of the Intermountain West.
What is the Mormon Corridor?
The Mormon Corridor is the area centered in Utah associated with Latter-day Saint settlements, boasting the highest concentration of LDS members in the U.S.
Which major rivers in this region reach the ocean?
The Columbia River and the Colorado River are the primary regional rivers that reach the Pacific Ocean.