RANGES OF SOUTHERN NEVADA 236 



thousand feet. This fault has determined a minor valley, but has no 

 primary effect on the topography. 



The Meadow Valley range, therefore, is a typical example of moun- 

 tains formed almost entirely by erosion, which has carved them out of a 

 series of gently folded and probably little-faulted strata. 



Las Vegas range. — This irregular group of mountains lies close to the 

 Meadow Valley range, and indeed passes into it at one point without 

 any intervening valley. It has in general a northwest trend, but there 

 is a branching ridge running due north and forming a V with the main 

 mass. Since this ridge, which is very high and bold, was not represented 

 on the maps, the writer called it, for convenience of designation, the New 

 mountains. 



The general folding in the Las Vegas mountains is a rough, shallow, 

 northeast-and-southwest-striking syncline, which is succeeded on the 

 west by a much sharper anticline, along which the narrow valley sepa- 

 rating the Desert and Las Vegas ranges has been eroded. The New 

 mountains seem to be separated from the westernmost ridge of the 

 Meadow Valley range by an anticlinal valley, which at its southern end 

 gives way to mountains uniting the two ranges. 



The rocks of the range consist of heavy limestones, ranging in age from 

 Cambrian to Carboniferous. North of Mormon wells there appears to be 

 a heavy east-and-west fault, which has brought the Carboniferous lime- 

 stone into contact with the Cambrian. The vertical displacement must 

 be several thousand feet, but it is marked by no scarp whatever, although 

 the minor topography changes, owing to the different (;haracter of the 

 two limestones. Bold scarps are frequent and even characteristic in 

 these mountains, but so far as could be seen they are not caused by faults. 



Recapitulating, the mountains possess synclinal ridges and anticlinal 

 valleys and have a heavy east-and-west fault which does not affect the 

 topography. They are, therefore, largely due to erosion. Since the trend 

 of the main fold is oblique to that of the mountains, the configuration 

 has not been entirely controlled by the structure. Las Vegas valley, 

 which lies on the west side of the range and separates it from the Spring 

 Mountain range, is wide and clear cut and runs at nearly right angles to 

 the folding. Topographically this valley is a branch of the valley of 

 the Colorado river, although actually it carries no drainage. If the cli- 

 mate should become moister, however, a stream w^ould at once establish 

 itself, and the aspect of the valley suggests that at a former period it 

 was carved out in this way. 



Spring Mountain range. — The Spring Mountain range shows a shallow 

 wrinkled syncline, with a northeast-and-southwest axis. This belongs 

 to the same series as the folds of the Las Vegas range, which are prob- 



