PREHISTORIC IRRIGATION PROJECT — SHETRONE 385 



leaps and bounds, with some 400 square miles of terrain, requiring 

 annually 1,000,000 acre-feet of irrigation water, now under cultiva- 

 tion. Thus the land of the ancient Canal Builders once more has 

 come into its own, and the Salt River Valley — the Valley of the 

 Sun — with its great citrus groves, date orchards, farms which pro- 

 duce as many as three crops annually, and subtropical plants and 

 flowers growing in great profusion, is indeed an oasis in the desert. 



In view of the fact that this transformation is due entirely to irri- 

 gation, it may appear contradictory to suggest that irrigation was 

 the principal cause of the downfall of the Hohokam peoples. The 

 Salt River Valley is underlaid with a "volcanic pocket" of clay or 

 marl which is virtually impervious to water. According to estimates 

 of the Salt River Waters Users Association, one-fifth of the total 

 irrigation water enters the ground as seepage, and builds up the 

 water table at the rate of from 3 to 5 inches each year. During the 

 period from 1870 to 1920, when irrigation was much less intensive, 

 one-third of the area under irrigation was rendered unfit for cultiva- 

 tion as a result of accumulated seepage and attendant alkalinity. 

 Under present-day intensive irrigation, the entire area, within a 

 comparatively short time, would be little short of an alkaline bog. 

 This threat now is averted by periodic flooding to eliminate alkali 

 and by using a battery of electric pumps for the purpose of removing 

 surplus water — some 300,000 acre-feet annually. 



The ancients had no drainage facilities, pumps or otherwise. The 

 result was inevitable ; surplus water and alkalinity, water-logged soil, 

 and dwindling productivity. This is evidenced by the fact that 

 exploration of the Pueblo Grande ruin demonstrated that the floors 

 of granaries and storerooms had repeatedly been elevated in an effort 

 to keep them above the water-logged surface of the ground. 



An additional situation, which may have been the coup de grace 

 of Hohokam survival, was the constant threat from marauding 

 nomadic tribesmen from the plateau areas. It is known that from 

 early historic times the agricultural peoples of the valleys were fre- 

 quently raided by the Navajo, the Apache, and other predators who 

 made bold to reap where they had not sown, and there can be but 

 little doubt that the peaceful Hohokam peoples, throughout their 

 sojourn in their chosen country, were forced to contend with similar 

 hostile incursions. Faced by such handicap, and seeing their once 

 fertile acres gradually transformed into water-logged and alkaline 

 wastes, it was inevitable that their numbers must decline to the point 

 where a few hungry stragglers either found refuge with other tribes 

 or passed entirely from the picture. 



Today there remain only the old canals and the ruins of once 

 impressive communal structures — mute evidences of a people who 



