Older Alluvial Fan 



Older alluvial soils are medium-textured and have moderately 

 or sometimes strongly developed subsoils. The parent 

 material of these deposits is alluvium that has washed from 

 mixed sedimentary hills of the Diablo Range. These older 

 fans have deeply entrenched drainage ways, so new material 

 is seldom deposited on the surface. Weathering and soil 

 development have caused formation of rather well-defined 

 soil layers. 



Basin Rim 



Parent materials of soils in this position are the same as 

 those of the older and recent alluvium; stratigraphy and 

 texture are often similar to the lower portions of the 

 recent alluvial fans. The prominent differences are soil 

 color and greater concentrations of salt in the soil profile. 

 Structural differences may also occur when salt concentra- 

 tions are predominantly the sodium ion. 



Soils in this position are usually fine-textured and are 

 generally characterized by moderate to extremely strong 

 concentrations of alkali in the soil profile. Salts accumu- 

 late at this position because of (l) leaching and runoff 

 from soils at higher elevations and consequent trapping in 

 depressions on the rim and (2) because of a long continuing 

 high water table under the basin rim soils. The second of 

 these is perhaps the most important. Evaporation at the 

 soil surface and transpiration by native vegetation brought 

 large quantities of salts into the surface soil and left 

 them there. 



Basin 



This group of soils comprises part of a large prominent 

 basin that extends nearly the entire length of the San 

 Joaquin Valley. Parent materials of soils in the basin 

 position result primarily from eluviation from mixed granitic 

 sediments originating in the Sierra Nevada on the east side 

 of the Valley that were deposited by waters of the San 

 Joaquin River, Fresno Slough, and the Kings River. Soils 

 which lie within the basin are easily distinguished from 

 soils in other positions. Basin soils are dark, fine- 

 textured, and poorly drained. 



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