io A Study of the Vegetation of 



the region. Snake River flows westward through the region in a 

 canyon which is simply an immense gorge a mile and a half to 

 two miles wide hewn in the basalt. Although 'the canyon is 

 over i, 600 feet deep, the river has not yet, except in a very few 

 places, cut to the bottom of the basalt, for its present bed is still 

 like its bluffs. The soil of these bluffs, as is characteristic of 

 similarly exposed situations in the region, presents various stages 

 of decomposition from the coarse talus at the foot of the cliff to 

 well formed soil. The canyon at its bottom is scarcely wider 

 than the river, except at the bends, where bars of moderate area 

 have been formed. The soil of the bars is partially river-sand 

 of granitic origin and partially wash from the bluffs. 



Except for the Clearwater, no large streams enter Snake River 

 in this region. Numerous small laterals have worked their way 

 back into the basalt, and it is along these that the main canyon 

 may be entered, especially from the south. 



In general, the topography is young. The streams have not 

 advanced far in their task of cutting away the rocks from the 

 plateau and of reducing the land to base level. Especially south 

 of Snake River, in Garfield County, where the surface is less roll- 

 ing, one is impressed with the view of a land with a broad plateau 

 surface and an infantile drainage. Here the spaces between the 

 streams are flat-topped. 



In the northwestern part of the area occur numerous small 

 lakes, of which Rock Lake, about 0.5 mile wide and 7 miles long, 

 is the largest. It is really a great crack in the basalt, with rocky 

 canyon walls and basalt bottom. It connects northward with 

 Little Rock Lake and is drained into the Palouse River by Rock 

 Creek. 



About these lakes, as well as along the canyons of the streams, 

 the weathering of the edge of the basaltic sheets has caused them 

 to recede unequally and to form steps or terraces in the faces of 

 the precipices. Where the walls are steepest, they present a 

 series of narrow steps covered with talus and soils in all stages of 

 formation, separating vertical masses of bare and frequently 

 columnar rock 30 or more feet in height (Fig. 45). 



In the drier western part of the region, where the disintegra- 



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