1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 397 



San Francisco River in 1882, comparatively small amounts of 

 mining detritus must have found their way into the irrigating 

 water-supply. Following the discovery, in 1893, of immense 

 deposits of low-grade sulphide ores in the district and the erec- 

 tion of concentrating plants to handle them, rapidly increasing 

 quantities of fine slimes were discharged into the stream-flow, 

 becoming noticeable in the irrigating waters of Graham County 

 about the year 1900. Following the observation of their pres- 

 ence, various crop failures were attributed from time to time to 

 the tailings, resulting finally in a request by the farmers of the 

 district to the writer, for an examination of the facts relating 

 to damage done by mining detritus to their irrigated crops. 



Solid Wastes 



Following this request, the writer began a study of the prob- 

 lem in May, 1904, which resulted in the publication of Bulletin 

 53 of the Arizona Agricultural Experiment Station, September 

 20, 1906. This publication established the fact that irrigating 

 sediments, in general, may be beneficial or harmful according to 

 their composition and physical character and to the manner of 

 their disposition in or upon the soil. If allowed to accumulate 

 upon the surface of the soil in the form of more or less im- 

 pervious silt-blankets, their influence, by limiting the supply of 

 water and air to the soil, is notably harmful. In the case of 

 the mining wastes from the Clifton-Morenci district, w^hich are 

 particularly plastic and "tight" in character, the damage done 

 was found to be greater than that resulting from sediments aris- 

 ing from ordinary erosion. It w^as determined that the damage 

 from these wastes, particularly to alfalfa and other crops which 

 cannot receive constant and thorough cultivation, was of an in- 

 creasingly serious character. 



The farmers of Graham Coimty, represented by one of their 

 number, finally brought suit against the Arizona Copper Com- 

 pany, Limited, for discharging tailings into their irrigating 

 water-supply. The case was decided in the District Court of 

 Graham County in favor of the farmers, and an order w^as issued 

 in November, 1907, effective May 1, 1908, restraining the mining 

 companies from discharging "slimes, slickens or tailings" into 



