4 CIECULAR NO. 124, BUREAU OF PLANT INDUSTRY. 



The mesa soil is a mixture of fine sand and gravel. It takes Water 

 readily at first, but after a few years of irrigation with the muddy 

 Colorado River water it becomes less pei-vious and tends to pack and 

 bake on drying. Tliere appears to be much less variation in tlie mesa 

 soil tlian in that of tlie valley. Except for a few hummocks, the mesa 

 is smooth, witli a gentle slope to the south and west. It Ues at the east 

 of the valley and is separated froni it by a steep slope. The native 

 vegetation on the mesa is very sparse, being limited to a few desert 

 shiTibs and some inconspicuous annual plants. The cost of preparing 

 mesa land for irrigation will be comparatively shght. 



About 10 per cent of the valley land on the Yuma Project contains 

 a sufficiently high percentage of alkah salts to render the growing of 

 ordinary farm crops precarious. These salts are composed chiefly 

 of chlorids and sulphates, with very little black alkali. It has been 

 found necessary to provide a drainage system to keep down the water 

 table to a depth from which the capillary action of the soil will not 

 carry the water to the surface. Such a system is now under con- 

 struction. 



THE CLEVEATE. 



The climate is warm throughout the year, the temperature for a 

 period of 35 years ranging from a minimum of 16° to a maximum of 

 120° F. Field operations can be carried on throughout the j'ear, and, 

 if it is desired to do so, the land may be used by growing crops prac- 

 tically all the time. The rainfaU is fight, averaging about 3 inches a 

 year, and is not a factor in crop production. 



There is marked difference between the temperature conditions on 

 the mesa and in the valley during the winter nights, when frosts occur. 

 The mesa is almost free from frost, even in the coldest weather, while 

 freezing temperatures are of frequent occurrence in the valley during 

 the \vinter months. Such comparative records as are available show 

 that the mean minimum winter temperature is about 9 degrees lower 

 in the valley than on the mesa. 



AGRICULTURAL DEVELOPMENT. 



Th(^ valley was fu'st occupied by iVmerican farmers in 1890. The 

 early agriculture was confined to the production of grain and alfalfa. 

 For many years the water supply was precarious and the danger from 

 overflow was such as to retard the permanent improvement of the 

 land. Since the construction of the protecting levees by the Recla- 

 mation Service and with the installation of irrigation works, which 

 insure an adequate supply of water, there has been more diversifica- 

 tion of crops, and much ])ermanent improvement has taken place. 



Notwithstanding many eiforts to estabfish other agricultural in- 

 dustries, the production of aKalfa has remained by far the most im- 



[Cir. 124] 



