THE CAHUILLA BASIN AND DESERT OF THE COLORADO. 7 



sea-level at Yuma to an average of 42 feet following the old shore-line of Cahuilla Lake 

 to — 2S7 feet, now partly submerged. 



FERTILITY OF THE DESERT SOILS. 



The Colorado River, like the Nile, is a great fertilizer of the land which it overflows. 

 Its alluvions are easy of tillage and are wonderfully productive. The Yuma Indians, 

 after the subsidence of a flood, find the land ready for the seed. Walking over the newly 

 deposited silt, a hole is made in it by the great toe, into which the seed-corn is dropped 

 and then covered with the ball of the foot. The corn sprouts and grows with great rapidity. 



The annual deposition of silt is constantly raising the level of the banks and increasing 

 the tillable area. This process has been going on since the elevation of the land above 

 the sea and the foundations of the Delta were laid. It is difficult to compute satisfactorily 

 the quantity of silt brought down by the river and added to its Delta every year. 



The Arizona Experiment Station made observations in 1904 indicating that the 

 lower Colorado carries approximately 70,000 acre-feet of silt on an average annually. 

 In the year 1904 the amount of silt in the river water varied from 84 to 3,263 parts in 

 100,000 parts by weight, and an acre-foot of water contained an average of 9.62 tons of 

 silt.' If it is assumed that one-half of the silt in the river water used for irrigation is held 

 in suspension until the irrigated lands are reached, a field to which 3 acre-feet of water is 

 applied would receive 14.43 tons of silt, which has an average value as a fertilizer of ap- 

 proximately $1.11 per acre-foot of water. Mr. H. T. Cory 1 gives the mean annual dis- 

 charge of the Colorado River as 17,070 cubic feet per second, and the mean total discharge 

 as 12,388,000 acre-feet. 



The fertilizing sediments from the annual overflow of the Nile, which stream has much 

 in common with the Colorado, are estimated at 6 inches of depth in a century. It is thought 

 that the bed of the river rises 4 feet in 1 ,000 years. It is said that 7 feet in depth of mud have 

 accumulated around the pedestal of the statue of Colossus, the date of which is about 1430 b. c. 



The French estimated the deposit of Nile mud, from Essonan to Cairo, at 5 inches 

 per century. The column of Rameses II is surrounded by a sediment 9.3 feet deep, fairly 

 estimated. This monument was erected 3,215 years before, which gives a rate of 3.5 inches 

 per century. But there are similar deposits below the depth of 30 feet, which, at the same 

 rate of deposition, would require 13,500 years to a. d. 1S54. 2 



ADAPTATION TO AGRICULTURE. 



Attention was early directed to the adaptation of the desert soil to agriculture, as 

 shown in the official report to the War Department in 1855. 3 



"The upper or gravelly plains of the Desert, especially those in the vicinity of the mouth of 

 the Gila, are too arid and wanting in soil to be ever used for agriculture. But this is not so with 

 a large part of the Desert— the part formed by alluvial and lacustrine clay. The whole of this clay 

 surface may be considered as capable of supporting a luxuriant growth of vegetation provided it is 

 supplied with water by irrigation. 



"The Cahuilla Indians in the northwestern part of the Desert raise abundant crops of corn, 

 barley, and vegetables in the vicinity of the springs at their villages. We also observed a dam at 

 the Cahuilla villages on the northern margin of the Desert, where we stopped over night. The 

 ground was principally clay, which by drying in the sun had become very hard, but on being cut 

 and pulverized by the passing of the train, became dry and dusty, like dry ashes. On cutting down 

 into it for about 12 inches it was found to be more sandy and micaceous. It appeared to be a rich 

 soil, for wherever water reached the surface the vegetation was abundant; and a large area near 

 the mountains was covered with a dense growth of weeds, the ground being moist. 



1 Proceedings of American Society of Civil Engineers, November 1912. 



2 Compiled from Draper's Intellectual Development of Europe, p. 87. 



3 Report Geological Reconnoissance California, Blake, and vol. v, Pacific Railway Reports, pp. 24S-249. 



