Basin and Range Province

The Basin and Range province has a characteristic topography that is familiar to anyone who is lucky enough to venture across it. Steep climbs up elongate mountain ranges alternate with long treks across flat, dry deserts, over and over and over again! This basic topographic pattern extends from eastern California to central Utah, and from southern Idaho into the state of Sonora in Mexico. What forces created this distinctive topography? The answer lies deep beneath the Earth’s surface...

Aerial view of linear valleys and mountain ranges that characterize the Basin and Range Province. Photo by ©Marli Miller

Within the Basin and Range Province, the Earth’s crust (and upper mantle) has been stretched up to 100% of its original width. The entire region has been subjected to extension that thinned and cracked the crust as it was pulled apart, creating large faults. Along these roughly north-south-trending faults mountains were uplifted and valleys down-dropped, producing the distinctive alternating pattern of linear mountain ranges and valleys of the Basin and Range province.
Although there are other types of faults in the Basin and Range province, the extension and crustal stretching that have shaped the present landscape produce mostly normal faults. The upthrown side of these faults form mountains that rise abruptly and steeply, and the down-dropped side creates low valleys. The fault plane, along which the two sides of the fault move, extends deep in the crust, usually an angle of 60 degrees. In places, the relief or vertical difference between the two sides is as much as 10,000 feet.

Hanaupah fault scarp, Death Valley National Park. This fault cuts like a knife across this alluvial fan, uplifting the mountain range relative to the valley floor. Many thousands of small uplifts and downdrops along faults like this are needed to create the basins and ranges characteristic of this province. Photo by ©Marli Miller

As the rocky ranges rise, they are immediately subject to weathering and erosion. The exposed bedrock is attacked by water, ice, wind and other erosional agents. Rock particles are stripped away and wash down the mountain sides, often covering young faults until they rupture again. Sediment collects in the adjacent valleys, in some places burying the bedrock under thousands of feet of rock debris.