GEE AT BASIN STRUCTURE. 25 



lie valleys. An ideal cross-section of the mountains and valleys of the 

 Great Basin is shown in the follovving- diagram: 



IV \ • • / 



FiLi. 1. — Ideal section illnstnitiug Great. Easiu atrnctiire. 



The structure here illustrated has been found so typical of the region 

 between the Sierra Nevada and the Rocky Mountains, that it has been 

 named by Gilbert the "Great Basin system" of mountain structure.'' 



The grandest displacements of the Great Basin are those determining 

 its eastern and western borders, i. c, the Wasatch and the Sierra Nevada 

 faults. The first has been described by King, Gilbert, and others, and has 

 been traced by the writer continuously for more than 150 miles; the second 

 has been studied at intervals for over 200 miles without determining its full 

 extent. The Sierra Nevada fault is much less regular in its course, and is 

 more complex than the corresponding displacement along the eastern border 

 of the Great Basin. It is conspicuous in Honey Lake Valle}^, California, 

 where its scarp forms a line of rugged cliffs, bordering the plain on the 

 west; and again along the west side of Eagle and Carson valleys, from near 

 Carson City southward for fifty miles or more. In the valley of Mono 

 Lake it is strongly pronounced; farther southward, in Owen's Valley, it has 

 again been recognized, but its southern, like its northern terminus, is at 

 pi-esent unknown. The details of this profound fracture are far from l)eing 

 understood, as it branches and changes its course in an extremely irregular 

 manner. Disregarding all minor dis|)lacements, as well as the results of 

 erosion and sedimentation, we may consider the Sierra Nevada in a general 

 way as the u})raised edge of an orographic block, having its eastern border 

 determined by the great fault we have noticed above. The desert region 

 stretching eastward from the base of the mountains is the thrown side of 

 the same displacement. It is on the depressed side of this fault that the 

 Lahontan basin is situated. 



» U. S. Geographical Surveys West of the 100th Meridian, Vol. Ill, p. 21. 



