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University of California Publications. [Geology 



Basalt. — The single area of rock mapped as basalt lies north 

 of Carson, and extends from the apex of a high ridge at an ele- 

 vation of 6,750 feet, to the valley near Empire. The flow lies on 

 rhyolite. The flow-planes strike northwest-southeast, and dip 

 southwest about 45°. In the field the basalt looks much like 

 that at Steamboat Springs, described by Becker. The rock is 

 in part massive and in part, near the top, very veseicular. Traces 

 of eindery and scoriaceous facies are present. The soil from the 

 basalt is intensely brick-red. A large portion of the top of the 

 flow near the valley slopes gradually downward and is fairly 

 unbroken. But as the higher slopes are reached much breaking 

 of the surface has occurred. The south face of the highest point 

 covered by the lava is very steep and covered with a thick coat- 

 ing of angular fragments. The form of this pile is that of a 

 large D, giving the name D Mountain to the summit. It is plainly 

 in evidence from Carson. 



Other Bocks. — The remaining rocks of the Superjacent Series 

 consist of lake beds, recent river gravels, and alluvium. These 

 would be of little importance were it not for the fact that they 

 are of value in deciphering the later geomorphy of the region. 

 The Carson lake beds, famed for its footprints, are little if at 

 all disturbed. Beds in Washoe Valley are tilted, however, as are 

 those near Reno. The lake deposits and beaches surrounding 

 Lake Tahoe offer a yet untouched field, and their bearing upon 

 later crustal movements is evident. The terraces of the Carson 

 River within the mapped area, and those of the Truckee near 

 Reno, are likewise important. All will be discussed in the 

 proper place. 



Eelative Age of the Superjacent Series. 

 Because of the bearing upon the series of orogenic disturb- 

 ances, the relative age of the later rocks, as far as can be de- 

 termined, needs mention. That period in the growth of the 

 range characterized by the various Tertiary eruptions was also 

 a time of intense diastrophism. The writer desires to urge the 

 use and value of these volcanic rocks in the study of this por- 

 tion of the range history. It is believed that a definite correla- 

 tion between the orogenic movements and lava flows over all the 



