I909-] THEIR CAUSES AND EFFECTS. 249 



In the Sierra Nevada, forming the eastern half of the state, 

 earthquakes are likewise frequent. In 1872 occurred the great 

 Owens Valley quake, which was one of the most severe on record 

 and was the result of movements producing- a series of faults along 

 a line more than 100 miles long with a throw of from ten to twenty 

 feet. This mountain system is formed of Precambrian granites, 

 gneisses and schists, upon which have been laid down upon the 

 west an unconformable series of late Paleozoic and Mesozoic strata. 

 The coast ranges, in which the earthquakes occur with far greater 

 frequency, are composed of a granitic core against which rest ex- 

 tensive Mesozoic and Cenozoic strata upon which are thick marine 

 Pleistocene and recent beds. The latter are full of the fossil shells 

 of still living species of mollusks and show that elevation is still 

 going forward in California. 



The San Francisco Peninsula is traversed by at least five known 

 lines or zones along which movement, or faulting, has occurred 

 again and again. The principal of these zones is the San Andreas, 

 which takes its name from an important lake through which it 

 runs. It is likewise known as the Stevens Creek fault, as the 

 Portola-Tomales fault or more simply as " the rift." This zone con- 

 tinues northwest in a slightly curved line to Point Arena and south- 

 east to the mountains west of HoUister. This is the continuous 

 extent of the fault, some 190 miles, but it probably extends under 

 the ocean beyond Cape Mendocino to the north and into the moun- 

 tains southeast of the line recently disastrously affected." Accord- 

 ing to H. W. Fairbanks^^ the recognized rift extends from Shelter 

 Cove, Humboldt County, as far southeastward as the Colorado 

 desert and is 700 miles long. Dr. Fairbanks states further that the 

 great Tejon earthquake of 1857 was caused by movement in the 

 same fault zone. 



The recurrence of horizontal and vertical movement along the 

 northern 200 miles of this fault line caused the earthquake which at 



" " The California Earthquake of 1906," by David Starr Jordan and 

 others. G. K. Gilbert, map, p. 317. San Francisco, 1907. 



'^ " The California Earthquake of 1906," pp. 321-337- See also " Report 

 of the California State Earthquake Investigation Commission," by A. C. 

 Lawson, chairman, p. 48. Washington, 1908. 



