158 CALIFORNIA ACADEMY OF SCIENCES [Proc. 3D Ser. 



the California interior somewhat centrally, presenting at the 

 same time magnificent stratigraphic sections that are unsur- 

 passed anywhere in the West in their exposures. 



Divisions of the Mount Diablo Range. 



Whitney divided the Mount Diablo Range into six more or 

 less distinct sections separated by certain low passes, some 

 of which at least are notable breaks in the range, and 

 though the region was not so well known then as now, it is 

 still useful to observe some of these divisions. 



The San Carlos Division of Whitney embraced that 

 portion of the range between the Panoche Pass on the 

 north and the Estrella (or Cottonwood) Pass on the south, 

 thus including most of the western border of Kings and 

 Fresno counties, or the territory adjacent to the Devil's Den, 

 Coalinga, and "Oil City" petroleum districts. It is this 

 division of the range which is chiefly the subject of the 

 present paper, the various features of which will serve to 

 illustrate the facts and conditions prevailing throughout the 

 range. 



Rocks of various kinds are found among the formations of 

 this section ranging in age from Paleozoic to Recent, and 

 embracing both sedimentary and igneous elements, though 

 the latter are of only minor importance. For the most part 

 the formations are arranged in roughly concentric fashion 

 about the two principal centers of this division, one of which 

 lies to the south and the other to the northwest of the 

 Coalinga district. On the eastern slope of the range the 

 structure is usually monoclinal, the strata dipping at varying 

 angles toward the Great Valley, generally toward the east or 

 north. The Cretaceous and early Tertiary beds stand at a 

 high angle, while the younger strata often have a much 

 ijentler inclination. 



The general topographic features of the Mount Carlos 

 Division of the range are similar to those of other portions, 

 and vary according to the underlying formations. The con- 

 centric arrangement of the rocks above referred to gives rise 

 to similarlv concentric series of hills and dales that have 



