MESA AND FOOTHILL VEGETATION 



19 



ravines. The explanation of this is simple. Water from snow and rain 

 in large amounts percolates into the mesa cap of coarse texture and finds 

 its way downward until it reaches the more impervious shales beneath. 

 It then follows this surface until it reaches the end or edge of the mesa, 

 where it forms a very definite seepage zone. This is shown in Fig 3. 

 This seepage finds its way into the small ravines on the sides of the 

 mesas but not into the soil of the ridges. 



In the gulches, between the mesas, the water content is high, much 

 higher than on the top or side. This wet zone, however, is narrow, 

 being little wider than the bed of the intermittent streams. 



2. Climatology of the Mesas near Boulder, Colorado 

 By Francis Ramaley 



Temperature and Rainfall. — The mesas under consideration are 

 located so near the city of Boulder that the records taken by the observer 

 in the city may be used to give a general idea of the climate. Summers 



TABLE I 



Summary of Data on Temperature and Rainfall at Boulder, Colo., for 

 Eleven Years Ending August, 1908* 



Month 



Normal 

 Mean 

 Tem- 

 pera- 

 ture 



Warmest Mean 

 on Record 



Year Degrees 



Coldest Mean 

 on Record 



Year Degrees 



Normal 

 Mean 

 Rain- 

 fall 



Greatest Rain- 

 fall on Record 



Year Inches 



Least Rainfall 

 on Record 



Year Inches 



Jan. . . 

 Feb..., 



March 

 April. . 

 May. . 

 June. . 

 July... 

 Aug... 



Sept. 

 Oct. 



Nov. 



Dec... 



Annual. 



34-i 

 32-9 

 39-4 

 47-7 

 56-4 

 64.6 

 70.1 

 71.0 



64.0 

 53-° 

 43 ° 



37-° 

 51.0 



1906 

 1907 



1907 



1902 

 1901 



1897 

 1900 

 1904 



1906 



39-° 

 42.8 

 48.1 



52-5 

 60.5 

 66.8 



75-3 

 73-2 



66.8 

 57-2 

 48.3 



41.0 



i9°5 

 1899 

 1906 

 1900 

 1907 

 1907 

 1906 

 1906 



1900 

 1905 



29-3 

 18.0 

 30. 2 

 45-6 



5i-° 

 62. 1 

 67.2 

 68.0 



61.5 

 48.5 

 38.1 



29.0 



0.4 



0.66 



1.6 



3-58 



3.02 



i-53 

 1.72 



i-3 



i-55 

 1.47 

 o-59 



0.68 

 18.0 



1903 



1899 



1900. 



1904 



1897 



1906 



1897 



1902 

 1903 

 1906 



1902 



1903 



1899 



1908 



1901 



1900 and 



1905 



1901 



1900 

 1899 and 



1901 

 1905 and 



1906 



0.08 

 0.09 

 0.23 

 1. 71 



o-SS 

 o. 29 

 0.46 



O. 22 

 O.IO 



0.13 



* The following additional data serve to show the extreme conditions. The highest recorded temperature 

 is 97 degrees, on July 15, 1902, the lowest is —20 degrees, recorded January 8, 1902, and again February 20, 

 1905. In 1906 the greatest rainfall was recorded, it being 26.17 inches, while 1901 was the driest year with 

 a rainfall of 13.67 inches. 



