436 SOILS. 



lower down than in the more clayey loam of the same locality, 

 and is more widely distributed in depth. 



Distribution of Alkali Salts in Heavy Lands. The mode of 

 distribution of alkali salts in the heavier, close-grained soil of 

 the Chino experimental tract in southern California, is illus- 

 trated in Fig. 67. This land is permanently moist, from a 

 water-table ranging from five to seven feet below the surface 

 in ordinary years. There is therefore no opportunity for the 

 formation of " alkali hardpan " as in the case of the Tulare 

 soil ; the salts always remain rather near the surface, viz. with- 

 in twelve to fifteen inches. But being in much smaller average 

 amounts than at Tulare (an average of about 5300 Ibs. per 

 acre), qui'te a copious natural vegetation of grasses, sunflowers, 

 and " yerba mansa " covered the whole surface, save in a few 

 low spots. 



A similar mode of distribution of the salts is found in the 

 still more clayey " black adobe " lands of the Great Valley of 

 California. The scanty rains cannot penetrate these soils to 

 any great depth, so that evaporation will soon bring the salts 

 carried by them back to within a short distance of the surface. 

 Their accumulation there is frequently indicated by the entire 

 absence of any but the most resistant alkali weeds, even though 

 the total of salts in the land may not be very great. 



Salton Basin. A peculiar state of things is illustrated in the 

 Salton Basin, which represents what was at one time the head 

 of the Gulf of California, and at the lowest point of which, 

 268 feet below sea level, there now lies a large deposit of rock 

 salt. It has been cut off from the present Gulf by the delta 

 deposits of the Colorado river, which now, however, overflows 

 into the Basin at times of extreme high water. Although 

 appearing level to the eye, the general slope of the country is to 

 the lowest point of the former sea-bottom. 



The region, now in progress of settlement by means of irrigation 

 water brought from the river near Yuma, was investigated with respect 

 to its alkali conditions in 1900 (Bulletin No. 140, Calif. Agric. Expt. 

 Sta). The annexed diagram 68 shows the distribution of the salts to a 

 depth of 21 feet. It will be noted that here also the alkali content 

 becomes insignificant at 4 feet depth, but increases again to a second 

 maximum at about 15 feet, below which there is a second decrease ; 



