153] FLORA OF BOULDER, COLORADO 5 



sandstones. The soft Lykins formation yields a very red soil. 

 The Jurassic and Cretaceous rocks have layers of sand and 

 clay. 



II. CLIMATE AND RAINFALL* 



The climate of Boulder, however enjoyable it may be to 

 human beings, can hardly be said to be highly favorable to 

 plant-life. At least this is true of the foot-hills, the mesas, 

 and the plains. The Main Range, however, is well watered, 

 but here the high elevation and the low temperature repress 

 plant-life. The montane and subalpine slopes have a dense vege- 

 tation, and yet even here the shallow soil and the rapid run-off 

 of the water cause portions of them to have the aspect of 

 deserts. A subalpine meadow has an opulent luxuriance ; an 

 adjoining slope may be gray with sage brush. In part the ap- 

 parent thinness of vegetation in the mountains may be due to 

 the superabundance of naked rock. In many portions of the 

 Rockies the greater part of the surface has no soil whatever, 

 and only a cranny-and-crevice vegetation is possible. The 

 Rocky Mountains are new; their rocks are sharp and jagged; 

 even lichens are rare on their surfaces. About Eldora and 

 Arapahoe Peak, however, the rocks are beautifully rounded 

 by glacial action. 



In the summer of 1906 there were rains almost daily, many 

 of them soaking rains, but their distribution was uneven and 

 capricious. In general the rainfall decreases as the distance 

 from the snowy range increases. The alpine and subalpine 



*For the climatology of the region, consult the article by Professor 

 Ramaley on the Climatology of the Mesas near Boulder, Univ. of Colo. 

 Studies, 6, 1935, also, the paper by Ramaley and Robbins on Redrock 

 lake near Ward, Univ. of Colo. Studies, 6, 13S147. 



