Southeastern Washington and Adjacent Idaho. 7 



in the western part of the area, is the basalt exposed. Westward 

 the soil becomes lighter in color, and in some cases is impregnated 

 with alkali. 



Calkins (i) has advanced the theory that the soils in many 

 parts of eastern Washington have been formed by wind action 

 and are not of a residual nature. His conclusion is based upon 

 the facts that in many parts of southeastern Washington there is 

 an absence of lamination in the soil, that it is extremely fine in 

 texture, that there is a remarkably sharp definition between the 

 soil and basalt, and that comparative chemical analyses indicate 

 soils not of the character naturally to be expected from the de- 

 composition of basalt in this climatic province. He believes the 

 principal source of the material was from the soft sedimentary 

 beds in the southwestern portion of the Columbia Plateau. How- 

 ever, the fact that there are no enclosed and undrained basins, as 

 there must be had wind been the only agent at work, leads one 

 to conclude that water erosion has also been an important factor 

 in forming the present topography. 



By the action of water, and especially the prevailing southwest 

 wind, the plateau has been moulded into rounded hills not unlike 

 sand dunes. The soils are constantly shifting from south and 

 southwest to north and northeast slopes. This gives better 

 weathering conditions on the exposed hillsides, while the soils 

 are deepest on the brows of the slopes where there is the most 

 favorable opportunity for the accumulation of wind-blown ma- 

 terial. 



As is characteristic of dry regions, the transition from soil to 

 subsoil is not well marked, although the lighter-colored subsoil 

 appears nearer the surface on exposed than on sheltered slopes. 

 The proportion of clay is greatest towards the tops of the hills. 

 Humus increases as one goes down the slopes and is highest in 

 the valleys, where it forms a rich, black loam. 



In contrast to the silt loam, grit-free soils covering the basalt, are 

 the sandy loam soils formed from the disintegration of quartzite, 

 granite, gneisses, and schists of the buttes and mountains. These 

 vary so widely in mechanical composition, water holding capacity, 



