Vol. IV] ANDERSON AND MARTIN— NEOCENE RECORD 51 



volves all three members of the Miocene series. It is flanked 

 on the southwest by some smaller folds of much less extent. 

 Faulting has taken place along and parallel to several of the 

 folds, but it is not prominent and needs no special considera- 

 tion here. 



The regional disturbances which have originated the fold- 

 ings along the San Juan River have developed at the same time 

 similar structures in many other districts within and probably 

 without the Temblor basin, as described in the first part of this 

 paper. 



Economic Geology 



The San Juan district is very largely devoted to stock rais- 

 ing and farming, and there are so far no industries based 

 upon any mineral deposits. There are, however, some deposits 

 of greater or less prospective merits and that may properly be 

 described here. 



Oil and Gas. — The San Juan district has been shown to 

 contain a good development of the formations which are oil- 

 bearing in other parts of the state and within the San Joaquin 

 Valley, and to contain also some favorable structures, such as 

 would appear attractive if located within the border of this 

 valley. 



Moreover, there are evidences of the escape of gases in the 

 past from the formations exposed at different points along the 

 San Juan River, and some slight signs of oil have been de- 

 tected in wells sunk into the bituminous shales to the west of 

 the river. These and other "indications" have induced some 

 prospecting to be done for oil, and many have regarded its 

 discovery in commercial quantities as a possibility, and this 

 will not be denied. 



However, the major folds in which oil could be stored have 

 been dissected in such a manner by stream action, that if oil 

 were present in large quantities it would be expected to make 

 itself evident in oil saturations of the surface rocks, or in ac- 

 cumulations of asphaltum at the surface. No oil has yet been 

 proved by actual drilling and wide areas on the flanks of the 

 anticlines from which large deposits could be derived are not 

 present. In other words the country available as a primary 

 source of oil is quite restricted, and from this point of view, 

 at least, commercial deposits do not appear likely. 



