SCIENTIFIC BACKGROUND 105 



of the basin as the bordering lands arose. This faulted 

 type of structure began along the west coast of Amer- 

 ica in middle Tertiary time, succeeding the folded type 

 of structure which accompanied the makings of the 

 Rocky Mountains in early Tertiary and Cretaceous 

 times. 



REGIONS WHERE FAULTED TYPES PREVAIL 



In some regions of the world, like the Dutch East 

 Indies and the west side of the American hemisphere, 

 the master faulting on a large scale prevails and con- 

 stitutes important elements in outlining the general 

 physiography. This is especially true of the Great 

 Basin Province of Eastern California, Nevada and 

 Utah ; of the Trans-Pecos Provinces of Texas, New 

 Mexico and Northern Mexico, and of California. In 

 fact, at least one California geologist holds that the 

 folding in this region is secondary to the faulting. 



It is the prevalence of faults in this Southern Cali- 

 fornia region which gives to it its marked physiog- 

 raphic individuality, the appreciation of which fact 

 has been long delayed, owing to the dominance of Ap- 

 palachian precedents in the minds of those who have 

 attempted to interpret the fundamentals of its geol- 

 ogy. 



It is a great mistake to look upon the fault lines 

 of Southern California with fear and forebodings as 

 dreaded sources of danger. Better to view them as the 

 causes of all the major conditions of our environment 

 — the makers of our highlands and valleys, the great 

 partition lines of the underground reservoirs which 

 store our oil and waters — in fact the fundamental 

 shapers of our surroundings to which the earthquake 



