522 CORRELATION OF DISTRIBUTIONAL FEATURES. 



Upper Sonoran Zone (fig. 39). — In this zone are comprised portions 

 of the Desert and more than half of the Grassland region. The ampli- 

 tude of the conditions is not, in general, as great as it is for either of 

 these two vegetations, since the zone does not include the more moist 

 half of the Grassland nor the extremely arid portions of the Desert. 

 This zone is largely one of arid grassland and comprises the Desert- 

 Grassland region of our detailed vegetation map. There is a wide 

 amplitude in length of frostless season and in number of cold days, 

 both seen to be characteristic of the Grassland, and there is a wide 

 amplitude in the number of days in the longest normal dry period. 

 Both the evaporation and humidity conditions range through wide 

 amplitudes, the former from 0.166 to 0.330 inch and the Latter from 

 40 per cent to 80 per cent. The most moist conditions in this zone are 

 to be found in the narrow strip which follows the coast of southern 

 California. 



Both the physiological temperature summation for the frostless 

 season and the moisture-temperature index show relatively narrow 

 amplitudes for this zone. The narrowest ones, however, are those . 

 exhibited by the number of days in the longest normal rainy period 

 of the frostless season and by the moisture ratios. The latter criterion 

 appears to express the conditions which are critical in the limitations 

 of this zone just as it does in the case of the Desert and Grassland. 



Carolinian Zone (fig. 40). — This zone bears about the same relation 

 to the Upper Sonoran that the Alleghanian does to the Transition. 

 That is to say, the temperature conditions are generally similar in the 

 two, while the moisture conditions are dissimilar. The temperature 

 similarity does not hold with respect to the length of frostless season, 

 as it did not in the case of the Transition and Alleghanian Zones. The 



Days in Normal FnosTtEsa ScASOit (F. SJ I 

 Hot Days, F. S. I 



Cold Days, F. S. I 



Physiological Summation, F. S. (Z 



Normal Daily Mcan. colocst 14 OAVs or Year C 

 Normal Daily Mean, Yeah C 



PftttlPITATlON 



Normal Daily Mean, F. S. C 



Days in longest Normal Rainy Period, F. S. 

 Days in longest Normal Dry Period, F. S. 

 Mean Totau Year 



Evaporation 

 Daily Mean. 1687-8, F. S. 



Moisture Ratios 

 Normal P/C, F. S. 

 Normal ff/E, F. S. 

 Normal P/E, Yean 



Humidity 

 Normal Mean, F. S. C 



Sunshine 

 Normal Daily Duration. F. S. CI 



Moisturc-Temrerature Indices 

 Normal P/E i T, F. S., Physiological Method I 



FiQ. 39. Climatic extremes for the Upper Sonoran Zone. 



