32 



University of California Publications. [Geology 



valley of Beet Creek, and seen from a distance they appear to 

 form the sharp gorge at the upper end of Beet Creek (fig. 3, 

 p. 37). 



The rhyolites evidently extend south from Thousand Creek 

 to the valley of Gridley Lake, where Heindl found them exposed 

 on the west side of the valley by a fault running northeast 

 and southwest, in a line nearly continuous with that of the fault 

 west of Mud Lakes to the north. The western Hank of Pine 

 Forest Range just to the east of Gridley Lake valley seemed 

 to Heindl to consist of an eruptive series similar to that exposed 

 in the fault-scarp on the west side of the valley. 



An outlying mass of rhyolite is also seen in a prominent hill 

 known as Antelope Butte, which rises above the lava-covered 

 mesa south of Virgin Valley (see fig. L p. 41). 



The rhyolites in these several regions are quite similar 

 petrographieally, they are always below the mammal-bearing 

 formations, they have experienced about an equal amount of 

 deformation, and there is evidence indicating that they belong 

 to the series of eruptives flanking the western side of the Pine 

 Forest Range ; so that they may all be considered as represent- 

 ing approximately the same horizon. From their occurrence in 

 gorges around the borders of Virgin Valley, these lavas may 

 be known as the Canon Rhyolite. They are presumably only a 

 portion of the extensive series for which the geographic appel- 

 lation of Pueblo Range Series is used. 



As was shown by Blake" the rhyolites of the Pueblo Range 

 are only the uppermost portion of a thick series composed largely 

 of basalts. In his mapping of the formations of southeastern 

 Oregon, Waring" has recently shown that the principal series 

 of lavas occurring over this region consists largely of basalts 

 followed in many instances by rhyolites. The rhyolites of the 

 Virgin Valley region are presumably only the upper portion of 

 this extensive formation. As has been stated by both Blake 

 and Waring, there is reason to believe that this series of erup- 

 tives is to be correlated with the great lava beds reaching over 

 a very wide extent of territory in the Columbia River region. 



s Op. cit., p. 214. 1875. 

 »Op. cit. 1909. 



