PLANT WORLD FOR NOVEMBER, 1919, WAS ISSUED MARCH 27, 1920 





SOME MOUNTAIN PLANT COMMUNITIES OF SANDY 



SOIL 



FRANCIS RAMALEY 

 University of Colorado, Boulder, Colorado : #*» 



I. PHYSIOGRAPHY AND CLIMATE 



The plant communities here considered occur in a limited area 

 of sandy soil near Georgetown in north-central Colorado, at an 

 altitude of 8500 feet. The city of Georgetown is located on Clear 

 Creek in a deep valley about a half mile wide. The canyon 

 walls rise quite abruptly 1000 to 3000 feet above the floor of the 

 valley. Various rock exposures occur: granites, gneisses, schists, 

 and some porphyry. Weathering of these rocks leads to various 

 degrees of disintegration and decomposition. Much of the 

 material is of a gravelly nature, having pieces of different sizes 

 intermixed. Again there may be a coarse sand or a sand and 

 gravel mixture. Such soil is common everywhere in the Rocky 

 Mountains and is known as "disintegrated granite." Below 

 Georgetown, however, there is an area in which the lower slopes 

 of the canyon walls are made up of pure sand of rather fine tex- 

 ture and with very little coarse material intermixed. A sample 

 of the sand was examined by Prof. R. D. George, of the Geology 

 Department of the University of Colorado, who states that some 

 of the sand, at least, is probably derived from mine workings or 

 stamp mills. Torrential rains, which sometimes occur, serve to 

 carry down a very large amount of loose material both of natural 

 and artificial origin. There is a likelihood also that some of 

 this sand is of eolian origin, being carried from the valley floor by 

 high winds of winter. 



The present paper records a study of the vegetation of this 

 sandy area (see map, fig. 1) which extends a mile along the west 

 boundary of the valley beginning about a half mile north of the 



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THE PLANT WORLD, VOL. 22, NO. 11 

 NOVEMBER, 1919 





