598 Thirty-second Annual Report 



the sources of the artesian waters are the lateral flows from the 

 sides of the valley and that the longitudinal movement in the 

 valley is quite negligible, except for the underflow in the Re- 

 cent deposits of the San Pedro flood plain. A similar study of 

 the Hereford artesian district has been begun. 



Knowledge of the relation of groundwater supplies in the 

 valleys of southern Arizona to the various components of the 

 valley fills has been handicapped by the uncertainty regarding 

 geologic relationship of the valley fills. Occasionally some essen- 

 tial information becomes available. For example, a well just 

 completed in Section 28, on the Rillito bottomlands four miles 

 northeast of Tucson, has penetrated 192 feet into the older 

 valley fill, which is believed to be of Pliocene age. The well is 

 420 feet deep, and is the deepest in the Rillito Valley. The 

 older fill at this point is pinkish-gray clayey silt and is uniform 

 in character throughout the depth penetrated. It is much in- 

 durated, with calcareous cementation, and is quite impervious. 

 Outcrops of the formation have been known for many years to 

 exist close to the base of the Santa Catalina Mountains. The 

 corresponding formations in the San Pedro and San Simon 

 valleys form the artesian caps of those districts. Until recently 

 it has been held that the Rillito Valley fill to great depth was of 

 Pleistocene age. 



ADDITIONAL WATER SUPPLY FOR THE UNIVERSITY 



CAMPUS 



For six years the University has been dependent upon a 

 single well situated in the basement of the Agriculture Build- 

 ing. It was imperative that an alternative supply be developed, 

 both to relieve the danger of water famine in case of a break- 

 down, and to increase the supply during the months of maxi- 

 mum demand. A site was selected near the east edge of the 

 campus and a well has been drilled to a depth of 320 feet. The 

 well has a concrete-lined pit to the water level with a station 

 room large enough for a pump and motor at that depth. Special 

 methods were used to insure the thorough development of the 

 well, and after completion a test indicated that the capactiy is 

 40 gallons a minute per foot of drawdown. A 2V2-inch motor- 

 driven pump of new design has been purchased, designed to de- 

 liver 400 gallons a minute on a lift of 130 feet. The pump, 

 though small, has a horizontally-split casing and single end 

 suction, and has a guarantee of 67 percent efficiency. 



