TOPOGRAPHY AND CLIMATE 



11 



of our local climates is due in the main to two great agencies, one 

 active, bringing heat, the other passive, shielding us from arctic 

 influences. 



First : Our proximity to the Pacific Ocean. Professor Alexander 

 G. McAdie, for twenty years in charge of the San Francisco office of 

 the Unted States Weather Bureau, and now Professor of Meteor- 

 ology at Harvard University, says of the mildness of the California 

 climate : "The Pacific Ocean is a great natural conservator of heat, 

 the mean annual temperature of which near the California Coast 

 ranges from 50 degrees to 60 degrees F. The strength of the west- 

 erly winds which prevail on the California Coast for more than half 

 the days of the year is due to the fact that the whole drift of the 

 atmosphere is prevailingly from the west to east. The climate of 

 west coasts is consequently less severe than the climate of east 

 coasts."* 



Second : Another agency contributing to the mild climate of the 

 Pacific Coast consists in the mountain barriers upon our northern 

 and eastern boundaries. It was Guyot who first called attention to 

 the fact that the Sierra Nevada and the Cascade Mountains reach 

 the coast of Alaska and bend like a great arm around its western 

 and southern shore, thus shutting off or deflecting the polar winds 

 that otherwise would flow down over the Pacific Coast States, while 

 California has her own additional protection from the north in the 

 mountain arch which has its keystone in Mount Shasta. 



CHIEF TOPOGRAPHICAL AND CLIMATIC DIVISIONS OF 



CALIFORNIA 



California is usually divided into three main areas and climates, 

 each distinct in typical conditions and yet separated by regions, 

 more or less wide, in which these conditions merge and influence 

 each other. Dr. Robertson says :f 



Isothermal lines which normally run east and west are, as they near the 

 Pacific, deflected north and south, and define three distinct climatic belts. 

 These may be named coast, valley and mountain; and while they resemble 

 each other in having two seasons, they are dissimilar in other respects. 

 These differences depend upon the topography of the country, and are of 

 degree rather than of kind; altitude, distance from the ocean, and situation 

 with reference to mountain chains, giving to each region its characteristic 

 climate. 



How similar are the conditions which prevail in these belts may 

 be learned from the data shown in the following table, which in- 

 cludes points separated by nearly the whole length of the State, the 

 difference in latitude of the extreme north and south points being 

 seven or eight degrees. Thus, through a north or south distance 

 great as that which separates the States of Georgia and New York, 

 similar climatic conditions prevail in California. In the following 



*"The Rainfall of California," University of California Publications in Geography, 1914. 

 tReport of State Agricultural Society, 1886, page 322. 



