the Muddy Mountains, Nevada, etc. 61 



silt, and clay was furnished by highlands which arose to 

 the south, and the enormously thick and , widespread 

 Jurassic sandstones w^ere probably derived from the same 

 source. All of the Mesozoic sediments indicate aridity 

 of climate. In post-Jurassic time the region suffered in- 

 tense folding, accompanied by overthrusting, probably 

 in connection with the Sierra Nevada disturbance. Dur- 

 ing the late Mesozoic and the first half of the Tertiary the 

 Muddy Mountain area was probably part of a high region 

 with exterior drainage, and received no deposits which 

 have been preserved. Intense normal faulting occurred, 

 and thick basin deposits were formed, probably in Upper 

 Miocene time. After erosion had subdued the topog- 

 raphy there was a recurrence of faulting which formed 

 new basins, in which thick deposits of saline silts and 

 clays accumulated. The present drainage system was 

 established later, probably in Quaternary time, and since 

 its establishment there have been changes of base-level 

 amounting to several hundred feet. Comparatively re- 

 cent disturbances have deformed late Tertiary and Qua- 

 ternary deposits, and it is possible that considerable fault- 

 ing accompanied these latest crustal movements. 



Bibliography. 



Ball, Sydney H. : A geological reconnaissance of soutliwestern Nevada and 

 eastern California, U. S. Geol. Survey Bull. 308, 1917. 



Buwalda, J. P.: Tertiary mammal beds of Stewart and lone valleys in 

 west-central Nevada, Univ. Calif. Publ., Bull. Dept. Geol., vol. 8, 

 No. 19, 335-363, 1914. 



Carpenter, Everett: Ground water in southeastern Nevada, TJ. S. Geol. Sur- 

 vey Water Supply Paper 365, 1915. 



Dake, C. L.: The horizon of the marine Jurassic of Utah, Jour. Geol., 27, 

 637-646, 1919. 



— The pre-Moenkopi (pre-Permian?) unconformity of the Colorado 



Plateau, Ibid., 28, 66, 1920. 

 Darton, N. H. : A reconnaissance of parts of northwestern New Mexico and 



northern Arizona, U. S. Geol. Survey Bull. 435, 1910. 

 Button, C. E. : Tertiary history of the Grand Canyon district, U. S. Geol. 



Survey Mon. 2, 1882. Also 2nd Ann. Ept., p. 126, 1882. 

 Gilbert, G. K. : The basin range system, U. S. Geog. and Geol. Surveys W. 



100th Mer., vol. 3, 1875. 

 Girty, G. H. : New species of fossils from the Thaynes limestone of Utah, 



Annals N. Y. Acad. Sci., 20, 239, 1910. 

 Gregory, H. E.: 'Geology of the Navajo country, U. S. Geol. Survey Prof. 



Paper 93, 1917. 

 Hill, J. M. : The Grand Gulch mining region, Mohave County, Arizona, U. S. 



Geol. Survey Bull. 580, 39-58, 1916. 



— The Yellow Pine mining district, Clark County, Nevada, U. S. Geol. 



Survey Bull. 540, 223-274, 1914. 

 Ives, J. C. : Eeport upon the Colorado Eiver of the West, Ex. Doc, 36th 

 Cong., 1st sess., 1861. 



