92 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



History, Science^ and Art 



esting places in tlie city. 



fine 



in 



an attractive and instructive manner. Tlie museum 

 authorities control the wonderful bone deposits (PL XXV, B) in 

 the asphalt springs of Rancho La Brea, about 8 miles directly west 

 of the city. Tlicse springs have been for centuries the most effective 

 natural animal trap known^ and the asphalt has preserved the bones 

 of the thousands of animals caught in its deceptive and sticky pools. 

 The skeletons of elephants, camels, sloths, saber-toothed tigers, bears, 



smaller 



XXV. ^). Among 



the bones has recently been found the skull of a human being who 

 lived probably not less than 10,000 years ago, contemporaneously with 



m 



northern 



5^ miles lung, covering an area of 2 square miles. Here 

 derricks have been erected in close proximity to dwelli 



& 



mgs. 



^ The following notes are based on a con- 

 cise account of the geology and technology 



Arnold and V. R. Garfias. 



Ralph 



The production of petroleum in Califor- 

 nia is the most Important mineral indus- 

 try in the State, the annual value of the 

 oil output equaling that of all the metals. 

 Since 1903, with the exception of 1907 

 and 1908, California has annually pro- 

 duced more petroleum than any other 

 State in the Union, and in 1914 the pro- 

 ductiou was over 100,000,000 barrels. 



The most prodnctiA^e fielda are in the 

 southern part of the great San Joaquin 

 Valley, which lies in the central part of 

 the State, and in the region along the 

 coast from the vicinity of Los Angeles to a 

 point a little north of Santa Barbara 

 County (fig. 13). 



Oil is found in commercial quantity in 

 geologic formations ranging in age from 

 Cretaceous to Quaternary. The princi- 

 pal formations are shown in the table on 

 page 94, the oldest at the bottom, the 

 youngest at the top. All these formations 

 are not present in any one region, and the 

 thicknesses given are rough estimates. 

 ^ In southern California the oldest forma- 

 tion containing oil in commercial quan- 

 tities is the Topatopa (Eocene), from 

 which wells in Shni Valley and at a few 



places in the Santa Clara River valley 

 obtain oil. The oil so far produced from 

 this formation is small in amount but it 

 is very light and brings a higher jM'ice 

 than any other oil in California. 



The shale of the upper part of the Mon- 

 terey group (Miocene) is the principal 

 source of oil in California and has yielded 

 oil in the Santa Maria, Santa Clara, and 

 Puente Hills districts. The gravity of 

 the oil ranges from 12^ to 35° Baurae. 

 This shale is made up largely of the re- 

 mains of diatoms — minute aquatic plants 

 composed of a Jelly-like substance sur- 

 rounded by a shell of silica. Only the 

 hard shells are now visible. They may 

 be seen with a strong magnifying glass in 

 the earthy varieties of this shale, the more 

 common forms appearing as flat disks 

 which look like minute percussion caps. 

 The soft matter is believed to have been 

 changed into petroleum. Besides the 

 diatoms the shale contains the shells of 

 minute animal forma called foraminifors, 

 the soft matter from which probably also 

 formed part of the petroleum. The oil 

 formed from these animals and plants has 

 moved into the sandy beds interstratified 

 with the shale, where it fills the spaces 

 between the sand grains; or into the 



flinty ehale itself. 



anes 



