548 C. R. KEYES PROFILES AND STRUCTURES IN DESERT RANGES 



Early Quaternary time. With the old Paleozoic beds are involved well 

 stratified clays and sands, 4,000 feet in thickness, presumably of Eocene 

 or Miocene age. A critical cross-section of the strata is one given by 

 Spurr of the Furnace Canyon, between the south end of the Grapevine 

 Mountains and the northern extremity of the Funeral range. For a 

 distance of more than 150 miles these two ranges form the eastern wall 

 of the deep Death Valley. The apparent low arch of Tertiary strata 

 may be due to near-by faulting of profound character rather than to the 

 action of compressive forces. The axis is parallel to the great fault-lines 

 bordering the Grapevine Mountains, and it is also near the principal 

 displacement plane in the Funeral range. The altitude of the inclined 

 Tertiary beds at the south end of the last mentioned ridge is also more 

 readily accounted for by faulting than by normal flexing. 



A hundred miles to the south of the last mentioned locality are Ter- 

 tiary beds the altitude of which is nearly vertical. This disposition of 

 the strata may be also due to faulting and not to folding. There are 

 other localities displaying the same phenomena, but in no instance at 

 present recalled can marked normal flexing be unqualifiedly ascribed. 



Character of the Older Tectonics 

 general features 



With the older tectonic features flexing is dominant. Eeversed as well 

 as normal faulting is of frequent occurrence. The geologic period dur- 

 ing which the most pronounced structures were acquired is believed to be 

 the Jurassic. All previously formed structures were then largely dis- 

 guised or obliterated. 



In arid America, outside of the Great Basin province, little reference 

 has been made to the older tectonics. Allusions to them in this area 

 have been not only few, but they have been incidental and general rather 

 than specific in character. King,^ in 1878, notes the mere existence in 

 some of the N'evada ranges of geologic structures formed before the pres- 

 ent mountains were reared above the plains. EusselP also makes passing 

 mention of similar phenomena in the same region. Considering the 

 main groups of ranges as probably outlined in pre-Tertiary times, when 

 the region was finally uplifted above the sea, Spurr® explains the present 

 features by assuming the early dissection of the country when there was 

 supposed to be greater precipitation than at present and when there 



* U. S. Geological Exploration of the 40th Parallel, vol. i, 1878, p. 715. 



s U. S. Geological Survey, Monograph XI, 1885, p. 26. 



8 Bulletin of the Geological Society of America, vol. 12, 1901, p. 266. 



