26 



dry farming precarious. In the Coast Ranges and on the Sierra 

 foothills are some successfully farmed residual soils but their total 

 area is relatively small. 



By far the larger portion of the agricultural lands in the state are 

 transported soils. For uncounted ages the winter rains have been 

 washing the rock fragments from the mountain sides and carrying 

 the material out to the valleys, spreading the mass out as broad 

 sloping alluvial fans or as relatively flat valley floor. The accumu- 

 lation of sediments in the valleys is often hundreds or even thousands 

 of feet deep (Fig. 1). 



Soils formed in this way may be quite uniform to great depths 

 or may be made up of successive layers of varying texture, sands, 

 silts, gravels or clays. As the soils are laid down a little at a time, 

 year after year, they have been acted upon by the weathering agents. 

 breaking up the particles and .making the plant food quite available. 

 Under the climatic conditions that exist, with the hot dry summers 

 and the low rainfall coming in winter, the weathering action of air 

 and water, the beneficial action of bacteria and the formation of humus 

 in the soil, occur to considerable depths. Roots ordinarily penetrate 

 to depths of six to eight feet below the surface. In studying the soil, 

 it is necessary to consider at least a six foot section instead of the 

 usual three foot section of the humid regions. The climatic conditions 

 of the region and the mode of formation of the soils, have brought 

 about many features that are not common to the soils of a humid 

 region. Owing to the lack of rain, the soils have never been subject to 



any degree of leaching and most 

 of the soluble materials have been 

 left in the soil masses. 



Hardpan. Where the soils are 

 old and have been subjected for 

 thousands of years to an annual 

 rainfall that has wetted the mass 

 to a depth of only two or three feet, 

 some of the soluble material has 

 been carried down and deposited, 

 cementing the grains together to 

 form a hardpan. In this way, the 

 iron and lime-cemented hardpans 

 common to the older, thoroughly 

 weathered, red and brown soils, 

 have been formed. In most cases, 

 the material beneath the hardpan 



SOIL 



HAROPAN 



SOIL 



Fig. 3. A hardpan layer with 

 loose soil material beneath it. Break- 

 ing up the hardpan will allow roots 

 and water to enter the substratum 

 of good soil. 



