Vol. 6] Merriam: Virgin. Valley and Thousand Creek. 



27 



with these aqueous beds. The beds were about 200 feet thick, 

 consisting of strata of white and red argillaceous rocks, rolled 

 conglomerate, and were all evidently formed from debris of 

 volcanic rocks, the conglomerate being made up principally of 

 rolled pumice. ' ' 



Blake pointed out particularly that the succession of igneous 

 rocks, in which basalts occurred below trachytes, did not agree 

 with Richthof en 's system. He also expressed the view that "the 

 geological formation of this range will be found to be repeated 

 in the vast outflows of volcanic rocks that cover so large a 

 portion of Eastern Oregon, extending north beyond the Columbia 

 River." 



No definite evidence of the age of any of the formations 

 was given by Blake, though he suggested that the erupted 

 rocks were early Miocene, and that the older rocks of the eastern 

 ridge were probably Triassic. 



Waring in his account of the Geology and Water Resources 

 of the Harney Basin Region, Oregon, refers to the work of Blake 

 and speaks of the Pueblo Mountains as "composed of rocks 

 that belong to an older series than do the lavas to the north. 

 These mountains were only cursorily examined, but from float 

 specimens that were collected along the eastern base of the 

 range they appear to be made up of andesitic porphyries, 

 micaceous schists, and granitic rocks, which have been more or 

 less extensively affected by mineralizing agents." 



In AVaring's paper on the Harney Lake region, the geology 

 of an extensive area to the north of Virgin Valley and Thousand 

 Creek has been outlined. Unfortunately the geologic mapping 

 was not carried to the southern end of the Harney Valley sheet 

 on Waring 's map, but was discontinued about twenty miles 

 north of the Oregon line. The northernmost point reached by 

 the University of California expedition in 1909 is situated near 

 the southern border of Oregon. 



The section at the southern end of the Pueblo Range was 

 examined in detail by Heindl in the ridge opposite Mud Lakes. 

 At this point a thickness of about eleven hundred feet in the 



« Waring, Gerald A., U. S. Geol. Surv., Water-Supply Paper, 231, p. 18. 

 1909. 



