Vol. IV] ANDERSON AND MARTIN— NEOCENE RECORD 25 



second part of this paper devoted to the Geology of the San 

 Juan district. 



Structures. — The Neocene structures now found in and 

 about the Temblor Basin, and illustrated by the structures in 

 the Mount Diablo Range, are the final result of far-reaching 

 geo-dynamic activity that has operated through several periods 

 and epochs of geological history. The general aspect of the 

 Geomorphic Map of California and Nevada shows the results 

 of compressional stresses that have acted from east to west in 

 the extensive wrinkling of the surface. This dynamic activity 

 probably began in Mesozoic time or earlier, but it is certain 

 that a large part of the distortion of the later strata was 

 effected in Tertiary or post-Tertiary time. In fact, as will be 

 shown later, much of it must have been accomplished in middle 

 or early Miocene time. 



The general effect of this activity or tangential thrust is 

 expressed in the Mount Diablo Range in two important ways, 

 each of which is better exhibited here than in any other part 

 of the basin. 



One of these effects is the widespread longitudinal folding 

 of the Tertiary and older strata along the flanks of the various 

 divisions of the range, as is to be seen in the several anticlines 

 and synclines along the eastern flank of the range and in and 

 about the oil districts, and on the San Juan River. 



Another effect is the breaking up of the main range into 

 orogenic blocks, as will be shown later, each having a more or 

 less independent diastrophic history. The structures herein 

 described are at one with, and dependent upon, the diastrophic 

 movements of the several blocks or divisions of this range, 

 and this is what should have been expected. An inspection of 

 the structures depicted on the maps of the Coalinga and McKit- 

 trick-Sunset districts shows a general system of folding which 

 involves all of the Neocene strata about the several oil districts 

 from Coalinga to Sunset. The principal folds, anticlinal and 

 other, follow a somewhat northwest to southeast course which 

 is in a measure parallel in all of the more northerly districts, 

 but which turns more easterly at the south. 



These foldings, as well as their grouping, will be seen to 

 have a definite and consistent relation to the faulting that has 

 taken place chiefly at right angles to the general axis of the 



