CROP ROTATION AND IRRIGATION" 117 



invested, and yielded a large profit, though it was often ob- 

 tained indirectly. India has the largest reservoir in the world. 

 It covers an area of 21 square miles, and it was constructed for 

 irrigating in Rajputana. It is known as the great tank of 

 Dhebar. 



Irrigation in the United States. In America, the town-build- 

 ing Pueblo Indian tribes practiced irrigation perhaps a thou- 

 sand or more years ago. Their ditches and canals can still be 

 traced in the little valleys near the mesas of southwestern Colo- 

 rado and adjacent portions of Utah, Arizona and New Mexico, 

 where the cliff dwellings are found, as well as across the bor- 

 der valleys through which are scattered numerous ruins of 

 community dwellings. Their knowledge of engineering is evi- 

 dent, and remarkable. Careful levels have been run over 

 several miles of their canals. The grade was found to be 

 fairly uniform and suited to a canal of such dimensions, as 

 well as in accord with present day knowledge of hydraulics, 

 safe velocities and coefficients of friction. While these well 

 defined remains of ancient irrigation works have long out- 

 lived the civilization to which they belonged, there are cases 

 where they have been utilized in modern works. The ditches at 

 Las Cruces, New Mexico, have been used uninterruptedly for 

 over 300 years. Some 70 years before the settlement of James- 

 town, the Spaniards irrigated on the Rio Grande. Adventurous 

 mission fathers pushed on to California, carrying the art of 

 irrigation with them. 



The beginnings of irrigation by English-speaking people in 

 this country were in the Salt Lake valley of Utah, in July, 

 1847. The Mormon pioneers, driven out from Illinois and Mis- 

 souri, stopped from necessity on the shores of the Great Salt 

 Lake. They diverted the waters of the little canyon streams 

 upon the present site of Salt Lake City, so that they might 

 raise a crop from the very last of their stock of potatoes and 

 save the band from starvation. At about the same time water 

 for irrigation was drawn from the ditches used for placer 

 mining by the gold miners of California. After the stoppage 

 of hydraulic mining by the passage of anti-debris laws, the 

 ditches were either abandoned or used exclusively for irrigation. 

 Many were enlarged and are still used. 



