304 Tw£;nty-seventh Annual Report 



It will be seen from the table that practically all of the Santa Cruz 

 run-off was absorbed into the ground and the residual tiow that reached 

 the Gila River was a small percentage of the total. The sum of the 

 Santa Cruz and Rillito discharges near Tucson in 1916 was 90,500 acre- 

 feet. Of this amount 64,900 acre-feet sank into the river bed between 

 the Tucson gauging stations and Sasco, a distance of 32 miles, while the 

 remaining 25,600 acre-feet passed Sasco. Just west of Sasco the stream 

 divides, part flowing northwest to Eloy and part west to an abandoned 

 reservoir and thence northwesterly to Maricopa. Of the former portion 

 the amount that reached Eloy was 4500 acre-feet. This amount is again 

 subdivided and probably less than one-third of it reaches the Gila. Of 

 the second portion only 2200 acre-feet reached Maricopa. 



The water table in the Casa Grande Valley, as studied by means of 

 wells, does not show so marked reactions to the periods of flood flow as 

 might be anticipated, and it is believed that to a considerable extent the 

 water seeps downward to depths of less than 40 feet and is returned to 

 the atmosphere through transpiration. Borings with a soil augur in 

 land recently overflowed indicatel a penetration of six feet or less. 



Slight effects on the water table are produced by seepage from the 

 Florence canal, while the irrigation of about 800 acres west of Casa 

 Grande appears to contribute considerably to the groundwater, thus 

 indicating an important result that may be expected if the San Carlos 

 dam is built and irrigation becomes general. 



The effect of pumping has been studied at those wells which are 

 most used. In general it may be said that interference can be noted for 

 distances up to one mile. Interference between wells is bound to be a 

 difficult ])r()blem in the future when the draught upon tiie groundwater 

 suppl}- is increased. 



THE ANTELOPE VALLEY 



A reconnoissance inspection of the Antelope \'alley was made Feb- 

 ruary, 1916. Contrary to .previous belief, this valley has great possi- 

 bilities of agriculture under irrigation. This is due mainly to the dis- 

 covery of excellent water-bearing gravels underlying the fine sands in 

 w^hich previous attempts have been made to obtain water for irrigation. 



The most difficult problem confronting the valley is that of pro- 

 tecting the valley lands from destruction by the great floods which occur 

 at infrequent intervals. At the outset there should be adopted a definite 

 policy of building homes on safe ground along the margins of the valley, 

 from which as a base the agricultural land can be workel Avithout danger 

 of a calamity. This is the European system, and is not only adapted 



