Agriculture 331 



ment widely distributed in the rocks of the earth, oxidizes to a 

 reddish color, and so gives a reddish-brown color to the soil. 

 The mineral element of humus is carbon, which is black in 

 color, and this gives a black color to the soil. Other minerals 

 oxidize to different colors, adding to the complexity of colors 

 in the soil and adding various plant food elements. Sodium 

 carbonate, or black alkali, is a common mineral in many soils. 

 It is soluble in water, and when it accumulates through lack of 

 sufficient drainage becomes a detriment in the soil. Sodium 

 carbonate is white in color, but as it combines with the tissues 

 of plants it burns or oxidizes these and leaves the black carbon 

 of the plants. It is therefore called "black alkali." 



A Great Variety of Seeds on a Variety 

 of Soils 



Onions are grown on an immense scale on Indio very fine 

 sandy loam in the Coachella Valley; lettuce abounds on what 

 is classed as Salinas clay soil in the Salinas Valley; in the River- 

 side area 90% of the very extensively grown orange crop is 

 grown on soils of sandy and gravelly type; and peaches, of 

 which there is a large acreage, are grown on soils which are 

 technically classified as sand (Hanford and Tujunga sands) . 

 Sugar beets are extensively grown on silt loam soils in this terri- 

 tory. In King and Tulare counties cotton thrives on the sandy 

 loam soils. In the Santa Clara Valley vegetable seeds are very 

 extensively grown on soils of heavier texture of the Yolo series, 

 soils that have been formed from recently-transported mate- 

 rials carried down from the sedimentary (or metamorphic) 

 rocks of the adjacent mountain slopes. Ninety-five per cent 

 of the lettuce seed, nearly all the radish seed, and 75% of the 

 onion seed, used in the United States are grown in this region. 

 About Auburn peaches constitute the largest commercial crop 

 shipped out of that area. The peach orchards are largely on 

 well drained sandy residual soils derived from granitic rocks, 

 technically known as Aiken clay loam. At Placerville pears on 



