TABLE 18 



MEANINGS OF MAP SYMBOLS USED FOR 

 DESIGNATING DRAINAGE SITE CLASSES 



NUMBERS 

 (Physiographic Positions] 



LETTERS 

 (Soil Permeability Profile Groups) 



1 - Alluvial fans on the west 

 side of the Valley, chiefly 

 from sedimentary sources. 



Moderate to rapid permeability 

 throughout without a significant 

 restricting horizon. 



Basin rim west of the trough. 

 Alluvium from sedimentary 

 sources . 



Moderate to rapid permeability to depths 

 ranging from 8 to 15 feet underlain by 

 a very slowly permeable horizon beneath 

 which may be strata of varying 

 oermeabilities . 



a/ 



Overflow deposits of coarse 

 and medium texture, adjacent 

 major channels in the valley 

 trough . 



- Dominantly fine-textured surface profile 

 or one having moderate development, 

 underlain by stratified alluvium with 

 combinations of slowly permeable horizons 

 and moderately to rapidly permeable 

 strata which will allow relatively free 

 lateral movement of significant volumes 

 of water. 



Trough and basin areas which 

 are the lowest positions in 

 the Valley. 



Fine-textured, slowly permeable surface 

 material, varying from approximately 

 ^ to 8 feet in depth, underlain by thick 

 strata of moderately to rapidly permeable 

 alluvium, often deep deposits of loose 

 channel sand . 



5 - Basin rim east of trough. 

 Alluvium chiefly from 

 granitic sources. 



Strongly developed (claypan and hardpan) 

 soils or those having a slowly permeable 

 unrelated substratum (the claypan, 

 hardpan, or substratum within 60 inches 

 of the surface), underlain by a combina- 

 tion of slowly permeable horizons and 

 moderately to rapidly permeable strata. 



Low anticlinal rldpcs. 



Mainly fine-textured alluvium with 

 tendency toward increasing density and 

 degree of compaction with depth. May 

 include some thick strata of rapid to 

 moderate permeability which do not 

 provide space for a significant volume 

 of water, and often pinch out within the 

 body of fine material. 



1/ Does not occur in the Drainage Site Classes in Figure Ip. 



67 



