(i 



University of California. 



[Vol. 3. 



Dr. H. W. Fairbanks thinks that we have in the Mohave 

 Desert essentially the same topography as characterized the site 

 of the Southern Sierra Nevada area before the great uplift to 

 which the Sierran valleys are due ; and also that the Sierra Madre- 

 San Bernardino Range is a portion of this old lowland which 

 was elevated by faulting at the close of the Pliocene period,* in 

 which view I concur with some reservations . As Antelope Valley 

 is a structural basin with a thick Tertiary and Quaternary filling, 

 I am not quite certain that the high range on its southern border 

 was not outlined during a disturbance prior to that which 

 opened the Quaternary era. Further, I suspect that some of its 

 higher and more broken portions represent residuals on the late 

 Pliocene plain such as are so common in the Mohave Desert, and 

 with as much reason may have remained in force on the oro- 

 graphic block which was subsequently thrust up into the present 

 high range. However, I will agree that the attitude of the 

 Upper Pliocene strata bordering on it and the many deep, 

 extremely narrow canons trenched into its mass, make it reason- 

 ably certain that the range owes its present great prominence to 

 uplift at the close of the Pliocene period. 



The Mohave Desert* and Antelope Valley were elevated as a 

 whole, without any great deformation, something exceeding 

 2,000 feet. On the north, the Tehachapi Range was thrust 

 up by the sharp tilting of a series of narrow fault blocks. At 

 the same time the Sierra Nevada Range rose to its present 

 prominence by the uplift of its eastern border to the extent 

 probably of from 7,000 to 10,000 feet. The disturbance 

 extended throughout the State. The Klamath Mountain region 

 was deformed into great domes and arches, with elevation 

 along the axes of several to the extent of 4,000 feet. The 

 Coast Range region was uplifted and deformed from end to end. 

 Among the best-known local evidences of this may be cited the 

 faulting, tilting, and erosion of the Merced series on the San 

 Francisco Peninsula and associated upthrust of Montara Moun- 

 tain as described by Lawson,t and the upthrust of Mt. Diablo 



* Communicated. 



tBull. Dept. Geol.. Univ. Calif., vol. 1, No. 4, pp. 148-151. 



