30 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTURE. 
necessary to put in occasional braces to hold them. The drainage of 
this tract could have been better accomplished by immediate drainage 
of the entire affected area, which includes several acres on the west, 
but the owner of the latter tract was not ready at that time. While 
the tract is not yet free from alkali, the surface has become fairly 
dry and the rushes have disappeared; however, the road on the west 
side of the tract still remains impassable. 
EXAMPLE IV. 
Twenty years ago the farm shown in figure 6 was considered one 
of the best in the vicinity of La Junta, Colo. The gradual rise of the 
water table and subsequent accumulation of alkali salts have seriously 
damaged 700 acres of land in this vicinity. Much of it is not farmed 
at all and none of it yields profitable crops. 
The tract is located in a circular basin which contains approxi- 
mately 3,000 acres, all of which is irrigated. Just below this traet 
the basin narrows down to a draw which bears north about 13 miles 
to a creek. This draw is the only feasible drainage outlet. There are 
two irrigation canals running through this district. More than 78 
second-feet are furnished to the land in this basin. Water runs dur- 
ing the entire year in one of the canals. The irrigation season is 
very long, and many people practice winter irrigation, which con- 
tributes largely to the damaging seepage water. The quantity of 
water used is no doubt considerably over 4 acre-feet per acre. 
The soil varies from a fine sandy loam to a sandy adobe. Gypsum 
is very abundant. It occurs in partly disintegrated crystals and 
flakes, often very nearly pure and imparting a mealy character to 
the soil. This constituent seems to have been derived largely from 
decomposition of the shales. A layer of gypsum always was found 
just above the shale and it seemed to carry water freely. On the 
south half of this tract, near the surface, is found a series of alter- 
nating beds of limestone and calcareous shales. The shales are very 
compact, and borings showed that while the upper layers, which had 
partly disintegrated and contained gypsum crystals, usually were 
‘moist, they became very hard and dry with depth. The water-carry- 
ing capacity of these shales may be considered as negligible. 
The idea is prevalent among the people of this section that the 
trouble is due to loss from the irrigation canals and that the proper 
method of drainage is to construct an intercepting line just below 
the canal. While these canals doubtless contribute to the under- 
- ground water, most of it is due to loss from laterals, to failure to take 
care of waste water, and to the use of excessive quantities of irriga- 
tion water. The injury due to excessive irrigation lies not only in 
the swamping of large areas of lower lands, but also in the ruin of 
large tracts from the accumulation of alkali salts on the surface. 
