Text Box:  Basin and Range Introduction | Causes of Formation | Volcanism | Climate and Drainage | Lakes | Death Valley | More National Parks | National and State Monuments/Features | Resources                                                     The Basin and Range province is slightly more than 300,000 square miles of very distinctive topography in southwestern United States.  The province extends from southern Oregon and southeastern Idaho southward through Nevada, western Utah, southeastern California, the southern half of Arizona, and central and southwestern New Mexico; it also includes a small portion of western Texas and northeastern California.  The general geomorphic characteristics of the province extend into northern Mexico.  Although the topography of the province is very different than that of surrounding provinces, several boundaries of the province are transitional.  Establishment of the northern boundary has been especially problematic.  Part of the northwestern section includes basalt flows that originated in the Columbia Plateaus province that flowed southward and have been faulted into structures similar to those of the rest of the Basin and Range, and thus have been included in the province.  (A few researchers place the boundary at the southern end of the flows.)  The province is divided into five sections: 1) Great Basin, 2) Sonoran Desert, sometimes called the Mojave-Sonoran Desert, 3) Salton Trough, 4) Mexican Highland(s), and 5) Sacramento (Sacramento Mountains).  The largest section is the Great Basin, which is essentially the northern half of the province, consisting of nearly all of Nevada and portions of adjoining states.  The term Great Basin is sometimes applied, incorrectly, to the entire province.    General Characteristics Fault-block Mountains The primary defining geomorphic characteristic of the Basin and Range is the occurrence of nearly parallel and relatively evenly-spaced fault-block mountain ranges separated by basins.  This basin-and-range topography is more extensively developed here than anywhere else in the world.  There are approximately 200 major ranges and a total of about 400 uplifted features.  Most of these trend generally northerly or northwesterly; a very small percentage trends toward the northeast.  These ranges are relatively shorter and not as tall as the majority of other mountains in the country.  In the northern part of the province the ranges have a maximum length of 150 miles and width of less than 25 miles–most are 50 to 75 miles long and 10 to 20 miles wide; summits are mostly less than 5,000 feet above the adjacent basins, although the relief at Wheeler Peak (13,063 feet in elevation) in eastern Nevada is much greater.  Many  ranges in the southern portion are less than 15 miles long and 4 miles wide, and elevation differences between summits and basin bottoms may be less than 1,000 feet.  Most of these faulted ranges are horsts, with normal faults on both of the long sides.  Many are not symmetrical but are tilted, with steeper eastern sides and more gently sloping western sides.  Geologist Clarence Dutton in the 1880s described this region as looking like “an army of caterpillars crawling northward out of Mexico.”  Many ranges have gently sloping surfaces at their bases; these are pediments (some geomorphologists now prefer the term benches) and they are especially well developed in the southern half of the province.  Pediments have been the subject of considerable research.  Most are exposed bedrock, which may be bare but is typically covered with a thin layer of material derived from the adjacent range.  Despite the usual presence of an alluvial cover, the primary cause of pediments has been determined to be erosion, not deposition.  There is no great uniformity among pediments, and it is most likely that different pediments have been formed by different combinations of processes.  However, there has been significant difficulty determining the exact causes:  “...more than 80 years of careful investigation has failed to generate a generally accepted model of pediment formation.”   Fault-block Basins Although there are more than 200 major ranges in the Basin and Range, basins comprise most of the total area of the province.  More than 50 percent of the northern half and more than 70 percent of the southern half consist of basins.  There are more than 100 individually-named basins in the northern half of the province.  The non-mountainous portion–basins coupled with the sloping surfaces (pediments) that are transitional between the basins and ranges–accounts for roughly three-fourths of the area of the province.  These basin-and-slope areas, generally found only in regions of internal drainage in this province, are referred to as bolsons, which often have extensive, flat, alluvium-covered central depressions.  Because of this aspect, this province is sometimes said to display mountain-and-bolson topography.  Basins are typically wider than the ranges, and many have very flat playas at their centers, consisting of material eroded and transported from the adjacent ranges.  Some basins have more than 10,000 feet of deposits.  Many of the basins of the province are grabens, bounded on both long sides by normal faults.  However, some basins have resulted from movement along just one fault; these basins, referred to as half-grabens, often have surfaces that are not as flat as grabens.     Basin and Range Introduction | Causes of Formation | Volcanism | Climate and Drainage | Lakes | Death Valley | More National Parks | National and State Monuments/Features | Resources