274 JOHN ERNST WEAVER 



Hills are composed of old crystalline rocks, quartzites and granite, 

 while the appended chains of buttes are almost wholly quartzite 

 in composition. All represent great elevations in the former 

 rough topography, which in rather recent geological time has 

 been flooded and most'y buried by the lava. The buttes are 

 islands of quartzite in a sea of basalt. The disintegrated basalt, 

 now a fine silt loam, has been moulded by the action of water, 

 and especially by the work of the prevailing southwest wind, 

 into a topography not unlike that of sand dunes. The rolling 

 hills with a height of 30-110 m. are characterized by much 

 steeper north and northeast leeward slopes. The soil is usually 

 deep, and only where the streams have cut channels among 

 the hills is the basaltic rock exposed. The wind likewise has 

 played an important role in carrying the finer particles of the 

 more sandy loam of the decomposed quartzites and granite to 

 the sheltered sides of the buttes and mountains. 



The more important plant associations occupying the basaltic 

 soil are few in number. The hills and narrow valleys were for- 

 merly covered with a characteristic prairie formation, only 

 relatively small areas of which now remain, while along the 

 exposed banks of the canyons this gives way to the bunchgrass- 

 rimrock association, and only on the more sheltered slopes of the 

 deeper canyons does the yellow pine occur. A poorly developed 

 shrub association consisting of Symphoricarpos race7nosus ,'^ Rosa 

 nutkana, Rosa pisocarpa, dwarfed specimens of Pi'unus demissa, 

 Crataegus brevispina, and Amelanchier spp. and sometimes Opul- 

 aster pauciflorus, and small trees of Populus tremuloides, occupy 

 areas on the more mesophytic slopes of the treeless hills. These 

 shrubs are better developed in the canyons and are usually fore- 

 runners (especially Opulaster pauciflorus) of the pine association. 

 Along the stream margins they give way to flood plain thickets 

 of Crataegus brevispina, Salix spp., Cornus stolonifera, Amelanchier 

 spp., and Alnus tenuifolia, or to small groves of Populus tremu- 

 loides, or, less frequently, Populus trichocarpa. 



^ The nomenclature throughout this paper is according to Piper's Flora of the 

 State of Washington. Contributions from the U. S. National Herbarium. 11: 

 1906. 



