224 W. A. CANNON 



this environmental characteristic is of moment will appear at 

 once when it is recalled that California may be said to be the 

 threshold to the desert, and, as for that, that much of the surface 

 of the state is, in fact, as arid as one can find anywhere. We must 

 bear in mind, therefore, that the capital response of the vegetation 

 in much of this great state is in association with the water relation. 

 As to the relative irregularity in the rainfall, the following ratios 

 of lowest to highest annual precipitation, based on the Weather 

 Bureau reports, are very striking. We find a variation of 1 to 

 to 4.3 at Fresno, in the Great Valley; a variation of 1 to 2.5 at 

 Eureka, on the northern coast. At Monterey the ratio is 1 to 4. 

 At Paso Robles, in the upper Salinas Valley, it is 1 to 5.5. Finally 

 at Indio, in the Colorado desert, the ratios is 1 to 26. Thus, in a 

 large portion of the state, perennials must experience, during a 

 not inconsiderable part of their life time, relatively severe droughts, 

 and accordingh^ we see the xerophytic element strongly empha- 

 sized. 



SPECIALIZATION IN TOPOGRAPHY 



As we view the state as a whole, we see that the greatest modify- 

 ing influences of the general climatic conditions are to be sought in 

 the mountain masses, which attain an extreme height of 14,500 

 feet in the Sierras, and in the other ranges an altitude of 9000 feet, 

 or less. In the mountains the temperature decreases and the 

 rainfall increases with rise in altitude, and these changes, when 

 not subject to the influence of local conditions, are fairly constant. 

 The mountains, further, operate to determine the character of 

 the climate of adjacent valleys. However, there are physio- 

 graphic features other than the mountains which are of importance 

 in bringing about specialized climatic conditions. A glance at 

 the topographical map shows that this must be true from the 

 state's physiographic complexit}^ Thus, there are isolated 

 mountains, or mountain groups. There are valleys separated 

 from other valleys by barrier ridges which have aspects in every 

 direction, and which are inland, or by the sea. There are broad 

 country-sides swept by the winds, which build up as well as modif>' 

 and destroy. There are detrital slopes of varying texture and 



