The Basin and Range province in Utah, Nevada, and California includes as its major subdivision the semiarid to arid region that has long been known as the Great Basin; it also includes, in southeastern California, parts of the locally poorly defined subdivision called by Fenneman (61)1a the Sonoran Desert and the Salton Trough. The boundaries of this region are in large part those established by Fenneman (62), but some departures have been made along the northern and southern boundaries, both of which are much less well defined than the western boundary, formed by the eastern front of the Sierra Nevada, and the eastern boundary, made up by western borders of the Wasatch Range and the Colorado Plateau. On the north a purely arbitrary line has been selected, which runs from Susanville, Calif., to McDermitt, Nev., and thence eastward along the northern boundaries of Nevada and Utah to the Wasatch Range. The southeastern boundary of the Colorado River is equally arbitrary, but the use of the San Andreas fault as the boundary on the southwest is perhaps as defensible as the irregular boundary heretofore used. The region thus bounded is shown on figure 10; throughout this text it is called, for the sake of brevity, the "Great Basin" or, simply, the "province."
These boundaries differ from the hydrographic limits set by Frémont (71) in the original definition of the Great Basin as the region from which no water flowed to the sea. A boundary drawn solely on the basis of drainage, however, would exclude a considerable area drained by the Colorado River that is geologically and topographically closely related to the undrained regions and would include part of southern Oregon that is geologically similar to the adjoining Columbia River Plateau.
According to Fenneman (61, pp. 342-343), the distinctive features of the Basin and Range province are "isolated, nearly parallel mountain ranges (commonly fault blocks) and intervening plains made in the main by subaerial deposits of waste from the mountains. These deposits, although locally absent, are often very deep and are generally unconsolidated. The consolidated older strata and lavas which make the mountains are locally horizontal. In general they are deformed and at places very much so." Although some may object to the implications of origin included in this statement, there can be little dissent to the distinctiveness, as compared with adjoining provinces, of the numerous individual mountain ranges which have been graphically characterized by Dutton as an "army of caterpillars crawling toward Mexico" and which are in general sharply separated from the intervening valleys.
Any summary of the geology of this great region is necessarily a statement of progress in the accumulation of knowledge and is based on rather inadequate data rather than on a selection of comprehensive observations and confident conclusions. The sources of information for a large proportion of the area are the hasty reconnaissance surveys made many years ago, and some large areas are still unexplored. Most of our present conceptions of Great Basin geology are therefore based on a few detailed studies of widely separated areas combined with the uncertain interpretation of older reconnaissance reports, and it is not surprising that the conclusions reached by different workers show considerable variance.
The present text emphasizes the more recent work in the region, but this more detailed work has, on the whole, far higher standards of accuracy. The recent publications cited, however, commonly include references to the older work.
Last Updated: 28-Nov-2007