36 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTURE. 
The land immediately northwest, north and northeast is irrigated. 
It is higher than the tract under consideration and is underlain by 
shale that outcrops in many places. As indicated on the map, a 
shale ridge extends from these higher irrigated areas, and the trouble 
first became evident over the backbone of this ridge and near the 
point. In des‘gning the drainage system one tile line was located 
so as to follow up the backbone of this ridge and one along each 
wigher Irrigated Land 
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Boundary of Affected Area__..2+ Pes, 
ae Height ebhove Datum...........—90— 
SCALE OF FEET 
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Fic. 10.—Twenty-acre tract near Grand Junction, Colo., showing plan of drainage. 
edge of the ridge. The system was installed in the spring of 1914. 
The tile were put at an average depth of 6 feet and connected with 
relief wells 2 inches in diameter that were bored into the shale to 
depths of from 6 to 12 feet below the bottom of the trench, where 
the water-bearing strata were encountered. One of these wells, of 
which there are 35, was installed every 17 feet, and practically the 
entire flow of water discharging at the outlet of the tile system comes 
from them. | 
