142 UNIVERSITY OF COLORADO STUDIES 



records of the observer at Long's Peak station, also at an altitude below 

 that of Redrock Lake, seem to correspond fairly well with those at the 

 lake. In preparing a problematical temperature curve for Redrock 

 Lake the data from Idaho Springs, Boulder and Long's Peak were used 

 with proper allowance in case of the first two. It is believed that the 

 curve presented in Fig. 6 indicates very nearly the mean temperature 

 by months at Redrock Lake. It is impossible to state, with the data 

 at hand, whether there is the same difference in winter and summer 

 between Boulder and Redrock Lake. As a rule in mountain regions the 

 high-altitude stations do not show relatively such low temperatures in 

 winter as in summer. 1 In a study of temperatures at Lake Moraine 

 and at Colorado Springs, Loud 2 found the difference in temperature 

 during winter was 11.7 and in summer 16.1 degrees. 



Length of Growing Season. — This may be very short. Thus in 

 1907 at a station (altitude 8,600 ft. or 2,620 meters) near Long's Peak 

 the date of last frost was July 16 and of earliest frost in autumn, Aug. '11, 

 leaving a period of less than one month without frost. Since, however, 

 there is a greater daily range of temperature at the Long's Peak station 

 it is likely that these figures would not be quite applicable to Redrock 

 Lake. Probably, as a rule, five or six weeks in the middle of summer 

 are without frost. This short time does not, however, represent the 

 entire growing season since the plants are all such as can withstand 

 light frosts. Other plants of the lowland districts would be unable to 

 exist there. 



Inversion of Temperature. — It is believed that temperature inversion 

 is not a factor of consequence at Redrock Lake. The temperature at the 

 shore of the lake is probably almost the same as that of the moraines 

 which shut it in. No doubt it is a very few degrees colder at night but 

 the day temperature is the same. In steep gulches it is probable that 

 temperature is of greater consequence as is shown by the marked differ- 

 ence in the flora of the sides and bottoms of gulches. In making a 

 preliminary study of this subject one of the writers made observations 

 for a week during August in a gulch of Beaver Creek about 5 km. 



1 Hann, Handbook of Climatology (Ward's Translation), p. 246, igo3. 

 • Loud, Colorado Sky, Vol. I, p. 8, 1908. 



