Region 1: The Basin and Range

The Basin and Range is the vast expanse of land that runs along the eastern edge of the Cascades and Sierra Nevada, down through Nevada, and toward the nation’s southwestern portions. It formed as the result of extreme tension on the continental lithosphere that underlies the Western US. A series of extensional faults led to the very prominent, zebra stripe-like pattern of sharp cliffs and wide valleys that make up the region’s topography.

The Basin and Range contains a vast watershed called the Great Basin (Figure 8.12), so named because it lacks an outlet for surface water. Although very little rain falls in this arid place, what does fall never reaches the ocean but instead drains into the valleys and collects in playa lakes, where it soon evaporates. This results in either dry soils or barren desert with sediment surfaces that have not become soil.

Figure 8.12: Extent of the Great Basin.

As a result of this harsh climate, Aridisols dominate the Basin and Range. One of the identifying characteristics of these soils is their inherent dryness. There is very little plant life in much of the region, so an organic soil horizon takes either a long time to form or does not form at all. Sediments that are introduced from weathered outcrops vary. More calcium carbonate-rich soils, called Calcids (a suborder of Aridisols), are common in the southern portions, while more silica-rich Argids (a suborder of Aridisols) are common in the northern areas. Traces of Mollisols and Entisols can be found around the edges of the region, and small amounts of Gelisols can be found in eastern Nevada.