240 



RALPH ARNOLD 



Pliocene occurs along the southwestern border of the San Joaquin 

 Valley in western Fresno and Kings counties where the Tulare 

 formation, largely of Pliocene age, attains a thickness of about 3,000 

 feet. 



DIASTROPHISM AND VOLCANISM IN THE PLIOCENE 



The most important movements inaugurating the Pliocene seem 

 to ha\e been an elevation of the Sacramento Valley and certain por- 

 tions of the coastal belt of northern 

 California and Oregon and the 

 closing of the connection between 

 the south end of the San Joaquin 

 Valley and the southern California 

 province. Although sedimentation 

 was practically continuous from the 

 Pliocene into the lowest part of the 

 Pleistocene over much of the Pacific 

 Coast, there is in parts of southern 

 California a sharp line of uncon- 

 formity between the Pliocene and 

 Pleistocene. The extreme localiza- 

 tion of the movements producing 

 this unconformity is well exemplified 

 at San Pedro, near Los Angeles, 

 where the Pleistocene is separated 

 from the Pliocene by an angular 

 unconformity at Deadman Island, 

 while half a mile distant on the 

 mainland the same formations are 

 perfectly conformable. Volcanic 

 activities of a more or less com- 

 plicated nature took place in certain 

 portions of northern and central 

 California during the Pliocene, while 

 in the same period and probably up 

 to a very recent date certain areas in the Sierra Nevada and Cascades 

 have felt the effect of volcanism to a marked degree. 



Fig. 5. — Map showing hypothetical 

 distribution of land and water on the 

 Pacific Coast during Pliocene time. 



