SOUTHERN PACIFIC LINES 249 
connection with the Boulder Dam project the supply will be provided 
by an all-American canal. (See p. 241.) The cost of the irrigation 
system in Imperial Valley has been about $18,000,000. The crops 
raised are most varied, with 112,432 acres of alfalfa, 22,165 acres of 
cotton (see pl. 37, B), and a large acreage of fruits and vegetables, 
including 8,000 acres in grapefruit and 70,000 acres in melons of 
various kinds. ‘he yearly value of its products is locally claimed to 
be between $40,000,000 and $50,000,000. Cotton, dates, citrus 
fruits, barley, and alfalfa grow side by side. From Imperial Valley 
New York gets its earliest cantaloupes, of which it is locally estimated 
that about 20,000 cars are shipped each year, and 15,000 carloads of 
lettuce were shipped to the eastern markets in 1926. The grapefruit 
crop in 1929, according to the United States Census, was 329,461 
boxes, and the grape crop 4,032 tons. Alfalfa yields 7 to 10 tons to 
the acre for each cutting, and it is harvested several times a year. 
Livestock and dairying are important industries which utilize the 
pasturage and forage products to great advantage. It is locally esti- 
mated that 16,000,000 gallons of milk was produced in 1929. 
The United States Department of Agriculture has made a detailed 
study of the soils of an area of 1,100 square miles in Imperial Valley, 
or most of that portion of the irrigable area that lies within the United 
States. All of the material is alluvium derived from the Colorado 
River, and although most of it is suitable for agriculture, some areas 
are too much mineralized for most plants, and others are suitable only 
for certain crops. Irrigation also adds to the mineralization unless 
precautions are taken to avoid accumulation of saline matter by 
evaporation, for river water contains considerable of it in solution. 
Imperial Valley has a very warm climate for a large part of the year, 
but temperatures rarely rise above 125°, and the mean is about 70°. 
With very low humidity the warmth is more bearable than sultry 
heat in other regions. In winter the minimum has been as low as 
19°, but temperatures below 32° are rare and of short duration. The 
mean annual rainfall is somewhat less than 3 inches. The climate in 
general is closely similar to that of much of the Nile Delta, but the 
average humidity is only about two-thirds as great and is much less 
variable. Dust storms, which occur mostly in February, March, 
and April, are short but trying. 
Prof. W. P. Blake, of the Government expedition of 1853, was 
probably the first to recognize the agricultural capabilities of the lower 
part of the Colorado Desert and to suggest that the water of the 
Colorado River could be utilized for its irrigation. A few years later 
river. In some years of scanty flow, | ments are 2,500 second-feet. (Homan, 
such as 1930 and 1931, Imperial Valley | P. T., Economic aspect of the Boulder 
could scarcely obtain a daily mean of | Dam project: . Jour. Economics, 
1,000 second-feet, although the require- | vol. 45, pp. 177-217, 1931.) 
152109°—33——_17 
