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lower Sonoran at the bottom to the Boreal at the summit 

 are compressed within this incredibly short distance. Eco- 

 logically one travels nearly five thousand miles while ac- 

 tually traveling only three, and the floral bands represent- 

 ing each zone are preposterously narrow. 



Animals are less rigidly confined to their special zones 

 than plants, and birds somewhat less than animals. Even 

 so, the fauna as well as the flora of a mountain slope often 

 tends to be confined very strikingly to particular zones. In 

 the mountains around Tucson, for example, one is not 

 likely to find jays below the level where the evergreen 

 oaks grow, or to find a gilded flicker much higher than 

 where these same oaks are just beginning to take over. 

 Some birds migrate upward a short distance in summer, 

 downward in winter, thus saving themselves the long jour- 

 neys taken by others who must change latitudes because 

 they have not convenient facilities for merely changing 

 altitude instead. Many animals also stick quite closely to 

 their own zone on the slope of a mountain, less because 

 they are sensitive to temperature than because it is only in 

 a particular zone that their food plants flourish. One will 

 find them isolated by desert lowlands or by peaks from 

 their fellows, whom one will find again at the same alti- 

 tude on another range. Thus a map of any considerable 

 mountain with the zones marked in color makes a S'ort of 

 biological pousse-cafe. Carried blindfold to an unfamiliar 

 region even a very moderately knowing student would 

 need only a glance about him to guess pretty accurately at 

 what altitude he found himself. 



To climb the east flank of San Jacinto is a bit of an 

 undertaking but the most sedentary can be shown what a 



