54 p. B. KING 



the early Pleistocene erogenic climax are especially striking in the 

 Ventura and Los Angeles basins of southern California, where thick 

 masses of Pliocene and lower Pleistocene marine and land-laid 

 strata are steeply upended, and are overlaid by nearly undisturbed 

 later Pleistocene deposits. This has been termed the Pasadenan 

 orogeny (Stille, 1936, pp. 867-870). 



The influence on the surface features of the varied faulting and 

 folding during difi^erent times since the beginning of the Tertiary 

 have been portrayed in many sets of paleogeographic maps prepared 

 by different geologists. The earlier, or mid -Miocene, deformation 

 shaped the ridges and troughs of the Coast Ranges into about their 

 present configuration, but left wide tracts of lower country still sub- 

 merged ; the later, or early Pleistocene, deformation produced wide- 

 spread emergence. During times of greatest submergence, the Coast 

 Range area probably resembled the present offshore region of south- 

 ern California, with shallow shelves, interspersed with much deeper 

 troughs, and linear islands that resembled the present Channel 

 Islands. During times of greatest emergence, the Coast Range area 

 probably resembled the present topography around San Francisco 

 Bay, with mountain ridges and intervening troughs or valleys, in 

 which land-laid sediments were being deposited, and whose lowest 

 parts, like the present bay, were covered by shallow, ramifying seas. 



SUMMARY 



Western North America is the region of the Cordilleran system of 

 mountain ranges, which extend inland from the Pacific Coast 400 to 

 1,000 miles to the Great Plains of the continental interior. The 

 landscape of the region has been shaped by surface processes of 

 erosion, sedimentation, and volcanism, but ultimate cause of the 

 features is deeper in the crust, in processes that have deformed the 

 rocks, brought about emplacement of magmas, and raised or lowered 

 large sections of the surface. These processes, though spasmodic, are 

 persistent through history. In considering the growth of a mountain 

 system such as the Cordillera, they may be generalized into a geo- 

 synclinal phase, an orogenic phase, and a post-orogenic phase. 



The geosynclinal phase was a time of sedimentation and rather 

 mild crustal activity. In the Cordilleran region it persisted through 

 Paleozoic time and through the first half of Mesozoic time. 



The orogenic phase began earliest in the western part of the 



