FOREST TYPES IN CENTRAL ROCKY MOUNTAINS. 



41 



For the stations below the control station the greatest excess of 

 temperature is recorded in the spring and summer months and the 

 least in winter; for the two stations at higher elevations the least 

 deficiency is recorded in the summer months and the greatest in 

 winter. This may be expressed more concretely. Although the 

 control station is almost midway between the highest station and the 

 lowest station in the series, its January temperature is 1.8° higher 

 than the mean of the two and its July temperature is 1.6° lower. 

 This is probably because of the high position of the thermometers 

 at the control station, although it may have a broader significance 

 than has been detected. Figure 3 shows the January gradient -as a 

 slightly convex curve, but the July gradient is not concave, the 

 control station only being depressed. 



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Fig. 3.— Temperature gradients in Pikes Peak region. 



More important is the fact that the altitudinal temperature differ- 

 ence is least in the winter months, reaching a minimum of 11.5° in 

 January and a maximum of 17.9° in April. The latter is plainly due 

 to the quick disappearance of any snow that may fall at the lower 

 elevations, while the high elevations suffer a handicap from the snow 

 blanket, which is only nullified through the summer. The small 

 difference in winter is probably due to the tendency of cold air to 

 settle at lower levels, which sometimes results in an inversion of 

 temperatures in the coldest weather. 



The January gradient amounts to 2.1° per thousand feet elevation, 

 the April gradient to 3.3°, and the mean for the year is 2.9°. It 

 should not be considered that these figures have any general value, 

 though they agree closely with the average of 10 Colorado watersheds 

 as computed by Ilobbins (20). 



