264 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



subsequently. King^ supposes that the fault-scarp of the 

 Sierra Nevada was formed either within the Eocene, or at 

 the close of the Eocene time, and was the direct cause of 

 the subsidence of the area which was soon after occupied 

 by the Miocene Pah-Ute Lake.'"^ King,^ however, also 

 states "that in Post-Pliocene times a very great orographi- 

 cal movement has taken place, the maximum displacement 

 being upon two lines: one upon the eastern base of the 

 Sierra Nevada, a region of long previously defined fault; 

 the other upon the western base of the Wasatch, also a 

 region of recurrent faults." 



The main Sierra Nevada fault-scarp is nearly continuous 

 from the south end of the range to Honey Lake. The 

 rocks forming this scarp are to a very large extent granitic 

 in character with subordinate amounts of schists of sedi- 

 mentary and igneous origin; but the entire series is of pre- 

 Cretaceous age. The remarkably fine scarp west of Honey 

 Lake appears to have been formed in late Tertiary or early 

 Pleistocene time, according to the investigations of Mr. 

 Diller; for at Thompson Peak and at other points on the 

 brink of the fault-scarp there are approximately horizontal 

 beds of Tertiary tuffs, and to the northwest of Thompson 

 Peak there is an extensive series of Neocene gravels still 

 preserved, resting at some points on the brink of the fault- 

 scarp. Lying to the west of this main fault-zone is another 

 of lesser magnitude extending from Lake Tahoe to Ameri- 

 can Valley, in Plumas County. This fault was studied by 

 Lindgren at Lake Tahoe and by myself at Sierra Valley 

 and American Valley. James Mills ^ also calls attention to 

 this line of faulting, one portion of which he designates as 

 the " Cromberg fault." 



ThQ basin of Lake Tahoe is regarded by Lindgren^ as 

 being a portion of a depressed block dropped down along 

 a double fault. This fault valley formerly extended from 



1 Fortieth Parallel Reports, Vol. I, 1878, p. 744. 



- Fortieth Parallel Reports, Vol. I, 1S78, p. 442. 



^This lake occupied a portion of the Great Basin east of the Cascade Range, and 

 King appears to consider that the Cascade Range was likewise separated from the Great 

 Basin by faulting along the same zone as that of the Sierra Nevada fault-scarp. 



4 Bull. Geol. Soc. Amer., Vol. Ill, 1892, pp. 418, 419. 



5 Journ. Geol. Vol. IV, 1896, p. 895. See also Truckee folio, U. S. Geol. Surv. 



