WHY CALIFORNIA CLIMATES ARE MILD 17 



mid-continental plateau on the other. Areas of greater or less atmos- 

 pheric pressure appear both over the ocean and over the plateau and 

 strive with each other for the joy of looking down upon the beauties 

 of California pushing, jostling and pursuing each other alternately 

 over protecting mountain barriers and wooing the modest maiden, with 

 heat or coolness, smiles or tears as are the fitful moods of ardent 

 lovers. 



Why Our Climates Are So Mild. Fortunately the suitor from the 

 ocean usually holds the points of vantage. Prof. McAdie says: 



"It is because of the general motion of the air from west to east 

 that the climate of west coasts is less severe than the climate of east 

 coasts. If the circulation of air were reversed, the Atlantic coast and 

 the middle portion of the country would have their temperature ex- 

 tremes much reduced and the climate would be in many respects 

 milder than that which now exists. On the other band, the climate of 

 the Pacific coast, and especially of California west of the Sierra, would 

 lose much of its present equability. The winters would be rigorous 

 and the summers very warm." 



As it is, the prevailing winds blow over a surface that is warmer 

 in winter and cooler in summer than a land surface would be. During 

 the summer the mean temperature of the ocean water is 60, and during 

 the winter 50 F.; while probably the extreme temperatures of interior 

 land-surfaces of the continent would frequently range more than 50 

 lower in winter and as much higher in summer and would produce in 

 California extremes against which the ocean is now our enduring 

 protection. 



Causes of Local Variations. But though these general causes are 

 always in operation and always formative, it is still true, as Professor 

 McAdie says: 



"In the diversified topography of the state we have perhaps the 

 most important factor in determining local climates. The state has a 

 mean length of nearly eight hundred miles and an average width of 

 two hundred miles. Its area is a little less than a hundred million acres. 

 The coast line corresponds in position with that portion of the 

 Atlantic coast extending from Boston to Savannah. The California 

 coast line has a mean annual temperature ranging from 50 to 60 F., 

 while on the Atlantic the ranging is from 47 to 68. In the winter the 

 difference between the mean annual temperature of the interior of 

 California and the coast is only about 5 F. but in summer the dif- 

 ference is more marked, amounting to about 20 F. The prevailing 

 westerly winds, wherever allowed access to the interior through gaps 

 in the Coast Range mountains, modify and practically control the 

 temperature," being however excluded from time to time, for short 

 intervals, by winds from the interior which surmount the Sierra and 



