CHAPTER XIX 



RANCHO LA BREA AND THE LOS 

 ANGELES BASIN 



The Los Angeles Basin is an unique part of the State of 

 California. It embraces an area of about 1,000 square miles. 

 The Basin is bounded on the northwest, north, and northeast 

 by the Santa Monica Range, the Verdugo Mountains and the 

 San Rafael Hills; on the southeast by the Repetto Hills; and 

 on the south and west by the Pacific Ocean. 



The mountains served as a source of detritus that was car- 

 ried by streams to the margin of the continent. What is called 

 the basin has been a basin for a long time. This "time" is rep- 

 resented by two great periods, the Miocene and Pliocene, and 

 indeed by a third period, the Quaternary or Pleistocene, which 

 immediately precedes modern or Recent time. Erosion of the 

 upheaved masses furnished the sediments that make up the 

 formations by which the basin has been filled. These sedi- 

 ments, originally laid down in essentially horizontal layers, have 

 been disturbed by deep-seated forces by which they have been 

 much folded and faulted. 



The present surface formations, of Pleistocene age, consist 

 of gravel, sand and clay, gravel being the most predominant. 

 Deep below the present surface are strata of gravel, sand and 

 shale, of Miocene and Pliocene age, having a total thickness of 

 11,000 feet, or more than two miles. This astounding thick- 

 ness of sedimentary deposits represents the "wash" from the 

 mountain highlands which border the basin on the north and 

 northeast, borne into the shallow sea, the bottom of which 

 slowly sank as the sediments accumulated. That this has been 

 a sinking coast during most of the long ages of Miocene, Plio- 

 cene, and Pleistocene time is attested by the great thickness and 

 character of the formations revealed in deep borings. 



