ABSTRACTS OF PAPERS READ JANUARY 2 551 



ORIGIN OF BASIN RANGES 



BY G. K. GILBERT 



[Abstracti 



Fresh interest in the origin of the Basin ranges having been aroused by Mr 

 Spurr's communication to the Albany meeting of the Society, the writer spent the 

 summer of 1901 in the study of certain ranges of western Utah. The paper dis- 

 cussed the origin of these as indicated by their phj^siography and structure, and 

 considered the nature of the evidence bearing on such questions. 



Evidence of block faulting was show^n to exist in extensive shear zones, in tri- 

 angular facets terminating the ridges in front, and in the even linear bases of the 

 ranges. That the faulting is still going on is shown by displacements in the recent 

 alluvium. 



BLOCK MOUNTAINS OF THE BASIN RANGE PROVINCE 

 BY W. M. DAVIS 



[Abstract] 



Observations of several of the Basin ranges in the summer of 1902 support the 

 opinion of Gilbert, Russell, and others that the ranges observed are carved in up- 

 lifted or tilted blocks of earth crust that had been previously much deformed and 

 eroded. The faulting of the crustal blocks has been continued into recent geolog- 

 ical time. The amount of erosion during the progress of faulting has been so 

 great that the pre-fault topography can not be safety determined. 



BASIN RANGE STRUCTURE IN THE DEATH VALLEY REGION OF SOUTHEASTERN 



CALIFORNIA 



BY M. R. CAMPBELL 



[Abstract] 



Recently attention has been called to the geologic structure of the mountain 

 ranges of Nevada and southeastern California. An attempt has been made to 

 show that they are generally anticlinal in structure, and that the tilted block tvpe 

 which Gilbert has described and which is generally known as Basin range structure, 

 is of rare occurrence. 



The object of the paper is to show that, although minor folding was observed 

 in the Death Valley region, the mountains are generally composed of huge blocks 

 of strata that have been strongly tilted and then eroded into their present forms. 



The region described is traversed by two systems of structures — one extending in 

 a north-south direction, being the southern extension of the true basin ranges of 

 Nevada, and the other crossing these in a northwest-southeast direction parallel 

 with and presumably an offshoot from the main line of the Sierra Nevada. The 

 movements wiiich -produced these structures seem to have been preceded by an' 

 epoch of slight folding in which the Paleozoic strata were somewhat deformed. 

 This was followed presumably in Eocene time by faulting and tilting along the 

 northwest-southeast axes which formed parallel mountains and valleys trending 

 n the same direction as the Sierra Nevada. In the valleys so formed lakes accu- 



LXXVI— Bull. Geol. Soc. Am., Vol, 14. 1902 



