76 



University of California Publications. 



[Geology 



Besides these there are a number of abandoned wells near 

 Chittenden just south of Shale Mountain. 



The La Brea anticline is very acute and is asymetric in form. 

 Hence the wells do not penetrate a great thickness of strata and 

 the logs are misleading in this respect. The upper oil sands are 

 all exposed on the surface by erosion and hence much of the oil 

 has escaped. There are doubtless several oil-bearing sands below 

 and the structure of the rocks is favorable for the location of 

 high-pressure wells. Deep drilling seems to be the only solution 

 of the problem. A thorough and accurate study of the structure 

 of the Lower Miocene rocks should materially aid in locating 

 wells, but no great production can be expected unless the wells 

 are drilled to depths of over 2000 feet. 



At the lower end of La Brea Canon, where the Sargent's Ranch 

 Oil Company is prospecting, the Lower Miocene oil-bearing rocks 

 do not appear on the surface and it is impossible to determine 

 the structure. The close proximity of Franciscan rocks at this 

 point, however, does not point to an anticlinal structure but 

 rather to a synclinal and it would seem that indications are not 

 favorable for large production. By working south, however, and 

 penetrating the fresh-water beds and San Pablo rocks, productive 

 fields may be encountered. 



The more reliable of the logs of the Watsonville Oil Com- 

 pany's wells on La Brea Creek are herewith published. It must 

 be remembered that the thickness of the beds indicated are 

 exaggerated owing to oblique penetration. 



Well No. 1. Record by C. A. Mitchell. 



Thickness Depth 



Material feet feet 



(Record missing) 591 591 



Blue shale 79 670 



Oil sand 34 704 



Brown shale (oil and gas) 566 1270 



Sand 6 1276 



Blue clay 64 1340 



Brown shale 26 1366 



Blue shale i 8 1474 



Brown shale 86 1560 



Oil sand (dry) 7 1567 



Blue clay 5 1572 



Brown shale (oil and gas) 31 1603 



Brown sandy shale (very rich) 12 1615 



Sand (salt water) 5+ 1620 



