PHYSICAL COMPOSITION AND CLASSES OF SOILS 



99 



also used to a considerable extent in the production of sugar beets. 



Arid Southwest. Gila Series. Light to dark brown soils of 

 flood-plain alluvium underlaid at varying depths by coarse sands 

 and gravels. Under favorable irrigation and drainage conditions, 

 the members of the Gila series are adapted chiefly to the produc- 

 tion of alfalfa, potatoes, truck, and root crops. 



Pacific Coast. Fresno Series. Light-colored soils with light- 

 gray, ashy subsoils and alkali-carbonate hardpan, derived from 

 old alluvial wash. Where protected from alkali accumulations, 

 these soils have been very successfully used for vineyards and 

 raisin grapes, and are particularly adapted to almonds, peaches, 

 and apricots. 



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Fig. 28. Photograph of a soil map, Willis area, Texas. 



Soil Survey. The soil surveyor is provided with a map, com- 

 pass, measuring instruments, and soil sampler. After a general 

 inspection has been made, and the provisional types decided upon, 

 the mapping is begun. Preliminary borings in the soil are made 

 to outline the location of a body of soil of uniform character. 

 This is then colored in on the map. The surveyor then works 

 away from this area until a different type of soil is encountered. 



