Basin and Range Province

Lore & Background

The Basin and Range Province includes much of western North America. In the United States, it is bordered on the west by the eastern fault scarp of the Sierra Nevada and spans over 500 miles to its eastern border marked by the Wasatch Fault, the Colorado Plateau and the Rio Grande Rift. The province extends north to the Columbia Plateau and south as far as the Trans-Mexican Volcanic Belt in Mexico, though the southern boundaries are debated. Common geographic features include numerous endorheic basins, ephemeral lakes, plateaus, and bolson valleys alternating with mountains. The area is mostly arid and sparsely populated, although there are several major metropolitan areas, such as Reno, Las Vegas, Salt Lake City, Phoenix, Tucson, El Paso—Ciudad Juárez, Mexicali, and Hermosillo.

Reader's Guide

The Basin and Range Province is significant for its distinctive topography, which results from tectonic extension and thinning of the lithosphere beginning in the early Miocene. The province's numerous ranges in the United States are collectively referred to as the 'Great Basin Ranges,' though many are not actually in the Great Basin. The tectonic mechanisms responsible for extension are controversial, with the most accepted hypothesis suggesting crustal shearing associated with the San Andreas Fault caused spontaneous extensional faulting. The province is also notable for its high heat flow, which lowers lithospheric density and stimulates isostatic uplift. Metamorphic core complexes in the province, where lower crust is brought to the surface, have provided valuable insight into extensional processes. The Basin and Range Province supplies nearly all the copper and most of the gold, silver, and barite mined in the United States.

Did You Know?

• The Basin and Range Province should not be confused with the Great Basin, a region defined by internal drainage that overlaps much of the greater physiographic region.
• Clarence Dutton compared the many narrow parallel mountain ranges to an 'army of caterpillars crawling northward.'
• The province's extension is widely attributed to mantle upwelling and gravitational collapse related to the same broad tectonic processes that cause narrow rift zones like the Afar triple junction.

Position Within the Intermontane Plateaus

The Basin and Range Province occupies the central and southwestern portion of the Intermontane Plateaus, one of eight major physiographic regions that make up the contiguous United States. This parent region is defined by its position between two great mountain systems: the Rocky Mountains form its eastern boundary, while the Cascade Range and the Sierra Nevada mark its western edge. Within this vast intermontane corridor, the landscape is dominated by alternating plateaus and mountain ranges. The Intermontane Plateaus are further divided into three distinct physiographic provinces. The Columbia Plateau Province occupies the northern reaches, the Colorado Plateau Province stretches across the southeast, and the Basin and Range Province fills the central and southwestern expanse. Each of these three provinces is itself broken down into smaller physiographic sections, creating a layered hierarchy of geographic classification. The Basin and Range Province thus sits at the heart of a region where the interplay of uplifted blocks and eroded plains creates one of the most distinctive topographic patterns in North America.

Tectonic Origins and Defining Mechanism

The Basin and Range Province is defined by a topography of alternating basins and ranges, a pattern that arises directly from crustal extension, also known as extensional tectonics. In this process, the Earth's crust is pulled apart rather than compressed, causing it to fracture along faults and creating a distinctive landscape of sunken lowlands bordered by uplifted blocks. This extensional mechanism is the fundamental geological force that gives the province its name and its characteristic shape. The province spans a large area across the Western United States, and the basin-and-range pattern is the dominant expression of this tectonic regime. This sets the Basin and Range Province apart from its two sibling provinces within the Intermontane Plateaus. The Columbia Plateau Province to the north is characterized by flood basalt eruptions from the Miocene and early Pliocene epochs, while the Colorado Plateau Province to the southeast is shaped by long cycles of uplift, faulting, and deep canyon erosion. The Basin and Range Province, by contrast, owes its form primarily to the stretching of the crust, producing a topography fundamentally different in origin from the volcanic or erosional landscapes of its neighbors.

Geographic Extent Across Two Nations

The Basin and Range Province covers a vast stretch of the American West, extending through all or portions of seven U.S. states: Oregon, Idaho, Nevada, California, Utah, New Mexico, and Arizona. Its reach does not stop at the international border. The province continues southward into Mexico, encompassing all or parts of the states of Sonora, Chihuahua, and Sinaloa, among others. This transboundary extent underscores that the extensional tectonics responsible for the province's formation operate across a continuous stretch of crust that political boundaries simply overlay. Within the broader Intermontane Plateaus, the Basin and Range Province occupies the central and southwestern portion, situated between the Rocky Mountains on the east and the Cascade and Sierra Nevada ranges on the west. The Sonoran Desert, identified as part of the Basin and Range Province, illustrates the diverse terrain found within its boundaries. The province's sheer geographic scale, spanning multiple states in two countries, makes it one of the most extensive physiographic regions in the Western Hemisphere.

Boundaries and Transition Zones

The Basin and Range Province does not end abruptly at its borders; rather, it transitions gradually into neighboring physiographic provinces. One notable boundary feature is the Mogollon Rim escarpment, which marks the transition zone between the Mogollon Plateau, part of the Colorado Plateau Province, and the Sonoran Desert, which belongs to the Basin and Range Province. This escarpment serves as a tangible geological boundary where two fundamentally different tectonic regimes meet: the extensional stretching that created the Basin and Range topography on one side, and the uplift-and-erosion history of the Colorado Plateau on the other. The Intermontane Plateaus as a whole are bounded by the Rocky Mountains to the east and the Cascade and Sierra Nevada ranges to the west, framing the Basin and Range Province within a corridor of plateaus and mountain ranges. The province's central and southwestern position within this corridor means it shares boundaries with both the Columbia Plateau Province to the north and the Colorado Plateau Province to the southeast, each of which is further subdivided into its own set of physiographic sections.

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