United States Geography

Article Outline

Introduction; An Expansive and Diverse Nation; Regions of the United States; Climates and Climatic Regions; Lakes, Rivers, and Coastlines; Environment and Society; More Information

The Intermontane Basins and Plateaus

The Intermontane Basins and Plateaus region is flanked on the west by the major Pacific coastal mountain ranges and on the east by the Rocky Mountains. In broad terms, the region consists of three distinctive subregions. The extensive Colorado Plateau encompasses parts of Colorado, Utah, Arizona, and New Mexico. The Columbia Plateau occupies eastern Washington, eastern Oregon, and southern Idaho. And the vast basin and range country lies between and around these two dominant plateau areas.

The Intermontane region is characterized by sparse population concentrated in a few major urban centers, a relatively isolated setting between extensive mountainous areas, varied topography, arid and semi-arid climate patterns, limited water assets, and considerable mineral resources.

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Natural Features

The geologic history within the Intermontane region varies by subregion. Basaltic lava covered the Columbia Plateau before a significant network of lakes deposited layers of silt. Faulting and warping created the present-day rugged and varied landscape. The Colorado Plateau features high plateaus and mesas dissected by extensive, steep-sided canyons. The remainder of the region consists of basin and range country, in which mountain ranges alternate with relatively flat basins. The mountain ranges are distinguished by block faulting, which gives them a rough, rectangular shape. The basins are characterized by features such as alluvial fans (soil or mineral deposits left by mountain streams that encountered flat terrain) and salt lakes. Perhaps the best known of these lakes is the Great Salt Lake.

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Economy

The region’s economy is based on irrigated farming, livestock grazing, mining, and tourism. The most critical resource for this region is water. Water for irrigation comes from the main rivers or from wells dug into aquifers (natural underground water reservoirs). Despite limited water resources, this region contains a number of major river basins, including the Colorado, Snake, Salt, Columbia, and the Rio Grande. The water of these rivers is used intensively. For example, the water of the Colorado River is so fully utilized for irrigation and urban uses that most of it does not reach its mouth in the Gulf of California. Irrigation in this region supports a variety of crops, including potatoes, apples, cotton, sugar beets, peaches, and cherries. Hay and grains are produced, often to support a scattered livestock trade that includes cattle, sheep, and goats.

Population

This Intermontane region has great cultural diversity. The Rocky Mountains are home to approximately 300,000 Native Americans, descendants of the original inhabitants. While Native Americans can be found in all states of the Intermontane region, they are concentrated in the Four Corners area of Colorado, Utah, New Mexico, and Arizona. This area is dominated by the vast Navajo Indian Reservation; the Hopi Indian Reservation also lies within its boundaries (see Navajo (People); Hopi).

The first European inhabitants of the area were the Spanish, who surveyed the region in search of mineral wealth. Southern areas—the states of Arizona, New Mexico, and Texas—border on Mexico and have large Hispanic populations. Street names, foods, and annual celebrations attest to strong historical links to Mexico. Many members of the Church of Jesus Christ of Latter-day Saints (commonly referred to as Mormons) live in Salt Lake City, Utah, and the church’s sphere of influence covers a much broader area. In the mid-1800s, Mormon farmers migrated to the area around Salt Lake City in search of an isolated area where they could practice their religion in peace. The rush to find gold and other precious minerals prompted sporadic movement into the area later in the 1800s.

In general, the Intermontane Basins and Plateaus region is sparsely populated with few significant urban centers. In the 1990s, the overall rate of population growth in the region was high, particularly in the southern regions, as people were increasingly attracted to the mild winters, recreational opportunities, healthful climate, and year-round sunshine. The region has a high immigration rate, both legal and illegal, of citizens from Mexico who move into its southern margins (see Mexican Americans). Border communities have swelled as millions of Hispanics crossed the border to settle in the region.

Historically, the population has remained scattered throughout the region until the last half of the 20th century, when many regional urban centers grew rapidly. The cities in the southern part have grown particularly quickly as increasing numbers of people are attracted to the dry, warm desert environment. Between 1960 and 1990, the metropolitan population of Las Vegas, Nevada, increased by six times, and that of Phoenix, Arizona, tripled. During the same time period, populations doubled in the metropolitan areas of Albuquerque, New Mexico; El Paso, Texas; and Tucson, Arizona.

The largest city in the region is Phoenix, Arizona, with a metropolitan population of 2.8 million (1997 estimate). Other urban centers include Salt Lake City, Utah; Tucson, Arizona; Las Vegas, Nevada; El Paso, Texas; and Albuquerque, New Mexico. These cities serve as regional market centers, and some of them also have specialized economies. For example, Las Vegas, one of the fastest growing urban areas in the United States with a population of 1.3 million (1997 estimate), is known for legalized gambling. El Paso, with a metropolitan population of 702,000, is closely connected economically and culturally with the neighboring Mexican border city, Ciudad Juárez. El Paso serves as a gateway and a destination for Hispanic migrants to the United States.

The California Region

This geographic region encompasses most of the settled part of the state of California, including the coastal area stretching from the northern border of Mexico to north of San Francisco. In the north, the region ends at the northern Coast Ranges, the Klamath Mountains, and the southern Cascades. The eastern boundary falls along the edges of the Sierra Nevada mountains and the Peninsular Ranges of Baja California. To the southeast, the region borders the desert lowlands of Death Valley and the Mojave Desert, and the area around the Salton Sea and the Imperial Valley.