326 Adventures in Scenery 



series. Soils of the old valley-filling deposits are formed by 

 weathering in place of the unconsolidated materials that have 

 been brought down from the hills by streams. These are classi- 

 fied into several series. Recent-alluvial soils have been derived 

 from materials washed down in recent time, and have not been 

 much affected by weathering. These also are grouped in sev- 

 eral series. Valley-filling soils are grouped into series on the 

 basis of age, represented by the degree of weathering, as young, 

 mature, or old. 



The soils of many provinces of the State have been studied 

 and classified by the U. S. Bureau of Soils and the State Experi- 

 ment Station. In the desert region of the Coachella Valley 17 

 soil types have been named. In the lava-covered region of the 

 far north, in the Big Valley area of Modoc and Lassen counties, 

 18 types have been named. In the Napa Valley no less than 

 52 types have been described; in the San Joaquin Valley, 

 Fresno area, 26 types. In the Placerville area, where soils have 

 been washed extensively for gold, 1 5 agricultural soil types have 

 been identified. In the Riverside area, representative of the 

 vast citrous fruit orchard lands, 36 types have been distin- 

 guished. 



Soils from Rocks 



The soils of all these regions have come from the rocks that 

 occur in those regions. In the mountain regions there may be 

 no soil, none having yet formed, or washed away as fast as 

 formed. On the slopes occur stony loam. Farther down the 

 slopes are soils grading in texture from stony loam through 

 gravelly loam, sandy loam, loam, clay loam, till finally the 

 particles of broken rock are so impalpably fine that the stone 

 particles are indistinguishable, and the soil is a clay. Thus in 

 texture soils range all the way from coarse fragments of hard 

 rock to plastic clay. So it is seen that soil is a form of rock. 

 It is a geological specimen. Its origin and character are deter- 

 mined by geologic processes. 



