28 



University of California Publications. [Geology 



upper portion of the series is exposed by a sharp fault along 

 the west side of the lake. The beds here dip at an angle of 

 about twenty degrees to the north of west. The section as 

 obtained by Heindl is shown in figure 1. 



rhyolite 



RHYOLITIC 



rurr 



BASALT 

 (SOLID) 



BASALT 

 (VESICULAR) 



Fig. 1. — Cliff section showing a portion of the Pueblo Range Series 

 immediately west of Mud Lakes. 



As nearly as can be determined the sequence here agrees 

 with that observed by Blake 7 . 



To the west of this extension of the range there is a con- 

 siderable thickness of ashes and tuffs resting upon the beds 

 exposed at Mud Lakes. Above these ash beds are still later 

 eruptives which Heindl believes to be rhyolite. This portion 

 of the section presumably corresponds to the upper portion of 

 Blake's section showing beds considered to be of aqueous origin. 

 According to Blake the beds of supposed aqueous origin were 

 conformable with the volcanic rocks below them, and were 

 covered by a layer of gray trachyte, also conformable. The 

 sedimentary beds consisted in part of conglomerate which was 

 made up largely of rolled pumice. 



Seen from some distance to the south, the great series of the 

 Pueblo Range eruptives and the associated beds appears as 

 a remarkable example of evenly tilted strata, extending back 

 toward the mountain core by regular steps as each hard 

 stratum is passed. The whole series runs under the plain of 

 Thousand Creek to the west with a fairly uniform dip of approx- 



7 Op. eit. 1875. 



