The Intermountain West is the broad, elevated region of the western United States that sits between the Sierra Nevada and Cascade ranges to the west and the Rocky Mountains to the east. It spans eight states: Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming. The region is defined by its high desert basins, dramatic plateaus, and the mountain ranges that hem it in on both sides, creating one of the driest and most geologically distinctive landscapes in North America.
Where the Intermountain West Begins and Ends
The name itself tells the story: this is the land “between the mountains.” The western wall is formed by the Sierra Nevada in California and the Cascades in Oregon and Washington. The eastern boundary is the front range of the Rockies. Everything in between, from the sagebrush flats of southern Idaho to the red rock canyons of northern Arizona, falls within this region.
Within those borders sit several distinct geologic provinces. The Basin and Range Province stretches across Nevada and into parts of Utah and Arizona, characterized by long, narrow mountain ranges separated by flat valleys. The Colorado Plateau covers much of Utah, northern Arizona, and parts of Colorado and New Mexico, home to the layered sandstone formations that define places like the Grand Canyon and Canyonlands. The Snake River Plain cuts across southern Idaho. These provinces look and feel very different from one another, but they share the common trait of being sandwiched between the continent’s two great mountain systems.
Why It’s So Dry
The Intermountain West owes its aridity to a process called orographic lifting. Moisture-laden air blows in from the Pacific Ocean and is forced upward as it hits the Sierra Nevada and Cascades. As the air rises, it cools and drops most of its rain and snow on those western slopes. By the time it descends into the basins on the other side, it has lost most of its moisture. This rain shadow effect leaves the lowlands of the Intermountain West with annual precipitation totals of just 5 to 15 inches in steppe regions.
The mountains within the region tell a different story. High-elevation stations like Alta, Utah, receive over 500 inches of snowfall annually, contributing to roughly 58 inches of precipitation in water equivalent. That snowpack is the region’s most critical water source, feeding rivers and reservoirs that sustain cities, farms, and ecosystems far below. The contrast is stark: a valley floor might receive 8 inches of rain in a year while peaks visible from that same valley get seven times that amount. This uneven distribution of water has shaped where people settle, where crops grow, and which ecosystems survive.
The Colorado River and Water Supply
No single resource defines the Intermountain West’s challenges more than water, and no single waterway matters more than the Colorado River. Seven states depend on it: Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. Between 35 and 40 million people rely on the Colorado River for some or all of their municipal water supply. Agriculture accounts for about 70 percent of the river’s total use. The United States also has a treaty obligation to deliver a portion of Colorado River water to Mexico.
Much of the Intermountain West lies within the Great Basin, a vast area where rivers and streams have no outlet to the ocean. Water that flows into the Great Basin either evaporates or sinks into the ground. This hydrologic isolation means communities in Nevada and western Utah can’t simply tap into a neighboring watershed when supplies run short. Water management in this region is a constant negotiation between growing populations, agricultural demand, and the reality that the climate delivers less moisture here than almost anywhere else in the lower 48 states.
Sagebrush Steppe and High Desert Ecosystems
The signature landscape of the Intermountain West is sagebrush steppe, a vast expanse of shrubland that once covered enormous stretches of the region. It is now one of North America’s most imperiled ecosystems, degraded by livestock grazing, development, wildfire, and invasion by exotic grasses like cheatgrass. Sagebrush provides habitat for a few bird species that cannot survive without it, including the Sage Thrasher, Sagebrush Sparrow, and Brewer’s Sparrow. These species depend on specific characteristics of sagebrush cover, including its height and the patchwork variation of shrub sizes across the landscape.
Beyond the sagebrush flats, the region supports a wide range of habitats that shift with elevation. Valley floors host desert scrub and salt flats. Mid-elevation slopes are covered in pinyon-juniper woodlands. Higher up, forests of Douglas fir, spruce, and aspen take over. Alpine meadows cap the tallest peaks. This vertical stacking of ecosystems within a relatively short horizontal distance is one of the Intermountain West’s defining ecological features.
Wildfire and a Warming Climate
Wildfire is a natural part of the Intermountain West, but the trend lines are moving in a troubling direction. An analysis of 1,469 wildfires in Utah alone between 1984 and 2021 found that a few large fires are burning increasing proportions of the total area burned each year. Temperature is a powerful predictor: the number of days per year when air temperatures reach or exceed 80°F explains roughly 31 percent of the variability in area burned, in both forested and non-forested landscapes.
Projections for mid-century are sobering. By 2050, warming trends in Utah could drive a 60 percent increase in area burned in forests and a 232 percent increase in non-forest ecosystems like sagebrush and grasslands. Longer fire seasons, hotter temperatures, and drier fuels are compounding the problem. For communities across the Intermountain West, this means more smoke-filled summers, greater risk to homes built near wildlands, and mounting pressure on the sagebrush ecosystems that are already struggling.
Indigenous Peoples of the Region
The Intermountain West has been home to Indigenous peoples for thousands of years. In Utah alone, five major cultural groups have deep roots in the landscape: the Ute, Shoshone, Goshute, Paiute, and Navajo. The state formally recognizes eight tribes, including the Northwestern Band of the Shoshone Nation, the Confederated Tribes of the Goshute Reservation, and the Ute Indian Tribe of Utah, among others.
Indigenous mapping of the region reveals overlapping territories and place names from multiple groups, reflecting the reality that Native peoples moved across large areas and interacted extensively with neighboring nations. Their knowledge of the land, particularly its water sources, plant communities, and seasonal patterns, shaped how the Intermountain West was inhabited long before European settlement and continues to inform land management today.
Economy: Mining, Energy, and Growth
The Intermountain West’s economy has historically been built on extractive industries. In Utah, energy and mining contribute over 10 percent of the state’s gross domestic product. The energy sector includes crude oil, natural gas, and electricity production. Mining encompasses coal, metals, and non-metallic minerals. Similar patterns hold across Nevada (copper and gold mining), Wyoming (coal and natural gas), and Colorado (oil and gas).
In recent decades, the region has diversified considerably. Utah’s Wasatch Front and Colorado’s Front Range have become technology and outdoor recreation hubs. Tourism is a major economic driver, with national parks like Yellowstone, Zion, Grand Teton, and Glacier drawing tens of millions of visitors annually. Cities like Boise, Salt Lake City, and Denver have experienced rapid population growth, attracting residents from higher-cost coastal areas. This growth puts additional strain on the region’s limited water supply and fire-prone landscapes, creating tension between economic expansion and environmental limits.
Living at Elevation
Most of the Intermountain West sits above 4,000 feet, and many communities are well above 5,000 feet. Roughly 400 million people worldwide live above 1,500 meters (about 4,900 feet), and a meaningful share of them are in this region. At moderate altitudes up to about 8,200 feet, the mild oxygen reduction may actually benefit cardiovascular health. But the effects are not uniformly positive. Children living at higher elevations face increased health risks related to lower oxygen levels during infancy and during respiratory infections. At elevations above roughly 8,200 feet, chronic exposure to thin air can lead to a condition marked by excessive red blood cell production, elevated blood pressure in the lungs, and persistently low oxygen levels in the blood.
For most residents of Intermountain West cities, which typically sit between 4,000 and 6,000 feet, the altitude is noticeable but manageable. Visitors from sea level often feel short of breath during their first few days, especially during physical activity. The combination of altitude, low humidity, and intense sun at these elevations means dehydration comes faster than most newcomers expect.