Mountains of the South 



at different times, and several times, is shown by the fact that 

 marine sedimentary formations now occur on the flanks and 

 top of the range. Fossils in the different formations prove un- 

 mistakably the age to which the rocks belong. An almost com- 

 plete succession of geologic formations representing the periods 

 from Triassic to late Tertiary time is revealed in the western 

 flanks of the range. 



The range was originally uplifted in (probably) Jurassic 

 time by upwelling from below of molten rock after the Triassic 

 rocks were laid down. The range has been raised and depressed 

 several times since. A great fault in the crust of the earth 

 marks the eastern foot of the range. The mountain block was 

 uplifted more on the east and was tilted toward the west. The 

 deep-lying granite has been brought up, and uncovered by 

 erosion, so that it is exposed at the surface on the flanks and 

 top of the range. The eastern slope of the range is therefore 

 steep and precipitous whereas the western side slopes more 

 gently toward the coastal plain. One mile south of Corona a 

 winding highway leads across the northern end of the range. 

 Following this highway through Mine Canyon and Black Star 

 Canyon a cross-section of the formations making up the moun- 

 tain may be seen. In Mine Canyon the bed-rock is metamor- 

 phosed Triassic slate. At the crest of the mountains a con- 

 glomerate and sandstone formation of Cretaceous age (Chico) 

 overlies the Triassic slates. The Chico formation is not meta- 

 morphosed, which means that the intrusion of the granite and 

 the metamorphism of the slates occurred in the great mountain- 

 building upheaval before the Chico formation was deposited. 

 This means further that the uplifted mountain range was 

 lowered nearly to or below sea level during the time when the 

 conglomerate sandstone formation was being laid down. The 

 road across the mountains passes through the Chico formation 

 to the contact between these Cretaceous rocks and the over- 

 lying Tertiary (Martinez) formation. On this northern por- 

 tion of the range several marine formations representing sue- 



