26 



University of California Publications. 



[Geology 



In the region investigated, five fairly distinct geologic 

 sections were examined; viz., those of Pueblo Range, Pine 

 Forest Range, Virgin Valley, Thousand Creek, and High Rock 

 Canon. For the purpose of description these sections are dis- 

 cussed separately. 



PUEBLO RANGE SECTION. 



Previous to the brief note published by the writer in 1907 4 

 the only reference to the geology of the region near Virgin 

 Valley known to have been published is that of Blake 5 , in 

 1875, on the Pueblo Mountains, extending southward along the 

 east side of the Thousand Creek region (pi, 2). 



Blake described a section of the beds across the Pueblo Range 

 which corresponds very closely in its upper portion with a 

 profile of the southern extremity of this range made by 

 A. J. Heindl, and confirmed by the independent observations of 

 E. L. Furlong and the writer in passing through this region. 

 According to Blake, the lowest formation is a "porphyry" 

 which is overlain on the east side by "metamorphic rocks, prin- 

 cipally micaceous and talcose schists with some metamorphic 

 limestones. These have a dip of about 78° E. with a strike 

 generally North 16° E. They appear to have been thrown up 

 by an eruption of porphyry, which now forms the crest of the 

 ridge." The western portion of the section is formed by a ridge 

 which overlaps the eastern ridge both at its north and south 

 ends. The western ridge was described as "composed entirely 

 of volcanic rocks, arranged in regular strata, with a dip of 20° 

 to the west. They form perfectly conformable layers, and extend 

 from its base to the summit of the ridge, a height of more than 

 1200 feet, 6,000 feet above the level of the sea. The beds are 

 composed of many varieties of volcanic rock." The section of 

 the western ridge consisted mainly of basalts below, with 

 trachytic rocks at the top. At the southern end of the ridge 

 Blake observed strata considered as of aqueous origin. "They 

 were laying perfectly conformable on volcanic rocks and were 

 covered in by a layer of gray trachyte also perfectly conformable 



* Science, n. s., 26, p. 380. Sept. 20, 1907. 



s Blake, J., Proc. Calif. Acad. Sci., 5, pp. 210-214. 1875. 



