686 SOILS: PBOPEETIE€ AND MANAGEMENT 



miles. In the Verde River valley in Arizona, remains 

 of the cliff dwellings, which were scattered long before the 

 advent of the Spanish explorers, are associated with ex- 

 tensive irrigation canals showing much skill. The ditches 

 and the reservoirs were finished with hard linings of tamped 

 or burned clay, and in one instance a main canal was cut 

 for a considerable distance in solid rock. Sometimes a 

 smaller ditch was sunk in the bottom of a large canal, to 

 facilitate the movement of small runs of water. The 

 ancient canals in the Salt River valley^ had a length 

 of at least 150 miles and were sufficient to irrigate 250,000 

 acres of land. 



In modern times the great Assouan dam has been built 

 on the Nile River, and with the associated reservoirs it 

 is designed to control the flow of the river and provide 

 water for irrigation. It stands as an example of present- 

 day irrigation development and control. 



590. Developmeat of irrigation practice in the United 

 States. —In the United States the earliest modern people 

 to practice irrigation were the Catholic missionaries in 

 southern California. The immediate predecessors of 

 the present irrigation systems in the United States were 

 built by a colony of one hundred and forty-seven Mor- 

 mons who went into the Salt Lake valley in Utah in Julv, 

 1847. The crops of these people were grown with water 

 diverted from City Creek, and their community life, to- 

 gether with their peculiar situation, led them to work out 

 in the succeeding decades the fundamental principles 

 of economic and social life as adapted to irrigation farm- 

 ing. In the last thirty years the practice of irrigation has 



1 Forbes, R. H. Irrigation in Arizona. U. S. D. A., Office 

 Exp. Sta., Bui. No. 235, p. 9. 1911. 



