The climate of most cismontane California, that is, of that part 

 of California lying west of the Sierra-Cascade crest, is a Mediter- 

 ranean one. The summers are cool and dry; the winters are rela- 

 tively warm and wet. There are even some genera, such as rock 

 rose {Helianthemum, Cistaceae), sage (Salvia, Labiatae), and tree 

 mallow {Lavatera, Malvaceae) that are common to similar climatic 

 zones of California and Mediterranean lands, though different 

 species occur in each of the two regions. 



The climatic influences of the ocean are manifold. Low pres- 

 sure areas that develop in the Pacific Ocean in the vicinity of the 

 Gulf of Alaska are stationary during some parts of the year, but 

 in the winter they frequently move southeasterly and bring cold 

 weather, strong winds, and rain to much of California. In the sum- 

 mer, these Pacific lows are generally centered to the northward 

 and as a result summer rainfall is rare in California, except for 

 local thunderstorms in the mountains. During the summer, the 

 moisture present in the cold oceanic air often condenses when 

 this air meets the warm, dry air from the land. The result is the 

 development of the coastal fog belt that is typical of much of the 

 Cahfornia coastline during summer months. 



In most of the central and eastern United States, climatic zones 

 tend to follow roughly latitudinal lines running from east to 

 west across the continent. In CaHfornia, however, the cUmatic 

 zones generally run in a more or less north-to-south direction. 

 This is due to the strong influence of the Coast Ranges and the 

 Sierra-Cascade axis: since these mountains run in a north-south 

 pattern, so does the climate over which they exert such a strong 

 influence. For example, the winter storms that bring rain to Cali- 

 fornia generally come into the state from the Pacific Ocean. The 

 distribution of this rain within the state, however, is largely 

 determined by topography. Much of the moisture in the Pacific 

 air is dropped by the time it reaches the crest of the Coast Ranges, 

 and a second portion of moisture is lost when the air reaches the 

 crest of the Sierra-Cascade ranges. As a result, one finds that the 

 immediate coast and the westerly slopes of both ranges have a 

 higher precipitation than do areas slightly east of each. Since the 

 Sierra-Cascade ranges are considerably higher than the Coast 

 Ranges, rather little moisture-laden air reaches beyond this 



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