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Chapter 21: Dry Regions: The Geology of Deserts
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The Rest of the Story: The Basin and Range Province
by Stephen MarshakTectonic stretching of the North American continental crust during the last 25 million years has yielded a broad rift called the Basin and Range Province, so named because topographically, it consists of long linear mountain ranges separated from one another by flat plains (basins) of alluvium. The high Sierra Nevada Mountains form the western edge of the province, while the face of the Colorado Plateau defines its eastern edge.
When the Basin and Range Province first formed, normal faulting yielding a series of tilted, faultbounded blocks. The wedge-shaped basins, or half-grabens, between these blocks quickly began to fill with alluvium that had eroded off the blocks. Bajadas covering the floor of the basins began lapping up the sides of the mountain ridges. Eventually, only the crests of the mountains remained, and these began to grow smaller because of scarp retreat and the formation of pediment. The pediments themselves have slowly been covered by alluvial fans. Thus, the ranges of the Basin and Range Province are rows of inselbergs, and the basins are alluvium-filled half-grabens. In some places, the centers of some of these basins have become playas or salt lakes. Overall, the floor of the Basin and Range Province lies low relative to its surroundings, so the province acts as an interior basin that geographers refer to as the Great Basin.
The Basin and Range Province experiences desert-like conditions because it not only lies in the rain shadow of the Sierra Nevada Mountains, but much of it lies far from the sea.Though dry throughout, variations in elevation and therefore temperature lead to major differences in the appearance of the landscape and the life it hosts. Thus, different portions of the desert are carpeted with scruffy, aromatic sagebrush. Others consist of playa (salt lakes), bordered by alluvial fans. Others are rocky landscapes dotted with a great variety of cacti and other desert conditions and unreliable water sources, the province presented a major obstacle to settlers heading to California. Only with the construction of the transcontinental railroad did crossing the Basin and Range Province become routine.
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