CHANNELED SCABLANDS OF THE COLUMBIA PLATEAU 619 



7. Scabland tracts are developed in pre-existing drainage lines 

 of the mature topography/ 



8. Scabland tracts are connected with each other.^ 



9. (a) The areas surrounded by scabland invariably have the 

 dendritic drainage pattern, mature topography and loessial soil of 

 the plateau, (b) They are almost invariably elongate with the 

 scabland tracts, (c) They commonly have steep marginal slopes 

 descending from 50 to 200 feet to the scabland. These slopes are 

 almost invariably in loess. Slopes of 30° to 33° are not uncommon. 

 They are much younger topographically than the slopes of the val- 

 leys among these mature hills. 



10. Scabland tracts with steep gradient are narrow, while those 

 with gentle gradient are wide. 



11. The pattern of scabland tracts, where hills of the older 

 topography are isolated in them, is anastomosing or ''braided." 



12. Scabland tracts invariably contain "channels." These 

 are gorges or canyons or elongated basins eroded in the basalt. 

 The channels are invariably elongate in parallelism with the tract 

 as a whole and, in most cases, the channel pattern is anastomosing or 

 braided. 



13. (a) Scabland tracts invariably bear discontinuous deposits 

 of basaltic stream gravel, (b) These deposits invariably contain a 

 small proportion of pebbles and cobbles of rock foreign to the 

 plateau, (c) These deposits invariably rest on an eroded, scabland 

 surface of the basalt, (d) They commonly lie on the down-gradient 

 side of eminences in the scabland. 



14. (a) Scabland tracts invariably bear scattered bowlders of 

 foreign rock, (b) The proportion of foreign debris, either the frag- 

 ments in the gravel or the scattered bowlders, is invariably smaller 

 with increasing distance down-gradient. 



15. Scabland tracts are invariably without a mantle of residual 

 soil. 



16. Scabland tracts are traceable up-gradient to a narrow basalt 

 plain bordering the south side of Spokane River in the northern 



' There are many exceptions to this rule, occurring where scabland tracts cross 

 pre-existing divides, but the total length of such is only a small fraction of the aggre- 

 gate length of aU scabland tracts. 



^ Moses Coulee is the onl}^ exception. 



