146 HORTICULTURE FOR SCHOOLS 



large river with a fairly continuous flow during the summer 

 season when demands for water are heaviest. 



The Imperial Valley is bounded on east and west by 

 mountains and on the southeast by the Colorado River. 

 Since the land slopes in a northwesterly direction from the 

 river to the Salton Sea, it seemed simple to divert a small 

 portion of the stream into canals and carry it over the valley 

 for irrigation purposes. One geological factor, however, the 

 builders failed to take into account. The Colorado River 

 flows along what has been described as the top of a hill. 

 Like the Mississippi, the water level of the stream is higher 

 than the adjacent country, with the resulting danger of 

 overflow in times of flood. In the northern end of the 

 Imperial Valley is the Salton Sea, a body of water between 

 two and three hundred feet below sea-level. In past cen- 

 turies the Colorado overflowed its banks, thereby cutting 

 a new channel, and flowed into the region of the Salton Sea. 

 When this region became filled with water, the Colorado was 

 again forced to send its streams to the Gulf of California and 

 in the course of time built up with its sediment a bank 

 which cut off the outlet into the Imperial Valley region. 

 This happened not once but many times, the region of the 

 Imperial Valley being successively an extension of the Gulf 

 of California, an inland lake, and a dried up lake-bed; this 

 process being repeated again and again. 



In the spring of 1906 the engineers in charge of the irriga- 

 tion project were repairing the intake which diverted the 

 waters of the Colorado into the Imperial irrigation system. 

 Unfortunately, the usual spring flood came this year several 

 months sooner than was expected, with the result that the 

 workers were forced to abandon the intake while it was 

 still in an uncompleted condition. A considerable portion 

 of the now swollen river immediately sought this new outlet, 

 flowing down through the valley and into the Salton Sea. It 

 Was only by most strenuous efforts and after the expenditure 



