PLANT COMMUNITIES OF SANDY SOIL 321 



Quadrat 4; short gras, 



Bare ground 75 



Bouteloua gracilis 20 



Chrysothamnus linifolius 4 



Mertensia lanceolata 1 



100 

 Quadrat 6; short grass 



Bare ground 85 



Muhlenbergia richardsonis 15 



100 



2. Plants of sand-gravel slopes 



In the steeper parts of the canyon walls having more than 30° 

 slope sand does not accumulate but is washed down farther to 

 the valley floor. There are, however, many slopes of mixed 

 sand and rock fragments. Here the shrub association is well 

 developed although somewhat differently from the way it is on 

 sand. The commonest shrub is not Symphoricarpos but Ribes 

 inebrians and there are not the large symmetrical clumps of 

 shrubs but smaller and more straggling specimens. The minor 

 species are much the same as seen in pure sand but more abun- 

 dant. Artemisia frigida, as would be expected, is quite common. 

 Grasses are largely absent. A few small trees develop on these 

 slopes, but only where the sand covering is thin and solid rock 

 comes close to the surface. The trees are Pinus scopidorum, 

 Apinus flexilis, and Pseudotsuga mucronata. 



8. Plants of rock wash 



At a number of points near the base of the canyon walls inter- 

 mittent or temporary streams have carried out coarse materials 

 upon the valley floor as "rock-wash" fans. The vegetation of 

 these fans depends much upon the coarseness or fineness of the 

 material of which they are composed. In well disintegrated 

 granite one of the rather early communities to develop is a Carex 

 grassland, chiefly a thin sod of Carex stenophylla. This well- 

 known community of foothill and montane parks (5) is repre- 

 sented especially on the fans derived from Silver Creek (see fig. 



