FARM ORGANIZATION IN SOUTHERN ARIZONA. 



mitigated by a very dry atmosphere, and sunstroke is unknown. The 

 nights are always cool, a range of 50° between day and night tem- 

 peratures being not uncommon during the summer months. The 

 following table shows the highest, lowest, and mean temperatures 

 for each of the months during 21 years at Phoenix, which is approxi- 

 mately the center of the irrigated section : 



Table I. — Temperature data at Phoenix, Ariz, for 21 years, 1S9G to 1916, inclusive. « 





Jan. 



Feb. 



Mar. 



Apr. 



May 



June 



July 



Aug. 



Sep. 



Oct. 



Nov. 



Dec. 



Highest 



°F. 

 81 

 16 



•P. 

 91 

 24 



o F 

 94 

 31 



°F. 

 102 

 37 



66.6 



°F. 

 114 

 39 



74.8 



°F. 

 116 

 49 



„ F _ 



117 

 63 



° F. 

 113 

 62 



°F. 

 112 

 49 



°F. 

 100 

 41 



°F. 

 92 

 28 



°F. 



80 





22 









50.0 



54.4 



60.5 



84.8 



90.4 



89.0 



81.4 



70.2 



58.7 



51.9 







a U. S. D. A. Weather Bureau, Summary of Climatological Data for the United States by sections. Sec- 

 tion III, and later annual reports. 



The rainfall averages about 7.27 inches per year. Most of the 

 precipitation occurs during two short rainy seasons, one in July and 

 August and the other during the winter months. The summer rains 

 are entirely local in origin and character, while the winter rains are 

 of a more general nature. The rains are seldom copious enough to 

 take the place of irrigation, and crop production depends entirely 

 upon irrigation for its water supply. 



There is abundant evidence that this valley was once irrigated by 

 ancient peoples, probably the ancestors of the semicivilized tribes of 

 Indians now living in or near the valley. Old canals aggregating 

 150 miles in length, have been located and it is estimated that at 

 least 140,000 acres were under cultivation at that time. Much of 

 the adobe and other heavy surface soils now found at different places 

 in the valley probably were deposited from muddy water used for 

 irrigation. 



The modern development of the valley began in 1867 with the 

 construction of the Swilling Canal. Between this date and 1892 a 

 dozen or more canals were constructed which were about equally 

 distributed between the north and the south sides of the river. 

 With but few exceptions the dams and headgates for these canals 

 were of a temporary nature and were washed out with every flood. 

 The dam for the Arizona Canal (see fig. 2), the largest one in the 

 valley, was the only one which had any semblance of permanency, 

 and it was partly washed out in 1891 and completely destroyed by 

 the floods of 1905. These conditions resulted in chronic water 

 famine. When the river was full of water there were no dams to 

 divert it to the land, and when there were dams in the river there 

 was not enough water to irrigate all the lands under the canals. 

 Water rights for 151,360 acres of land were adjudicated in 1889, 



