220 IRRIGATION INVESTIGATIONS IN CALIFORNIA. 



a distance of 20 miles from that place, where the river runs into the Fresno Swamp 

 delta. 



The entire face of the valley trough surrounding the Fresno Swamp and the 

 great bend of the San Joaquin River is often submerged during the floods, and below 

 this region numerous sloughs break out from the San Joaquin, and, after running 

 for a distance in the same general direction, reunite with it lower down, thus form- 

 ing a broad, swampy area, often submerged and generally very fertile. 



From Pollaskj- the river flows over alternating beds of disintegrating granite, 

 interspersed with bowlders and coarse gravel and broad, flat bars of sand. Its 

 channel varies in width from 300 to 900 feet, and also greatly according to the stage of 

 the river. Its descent from PoUasky to the lower plains below Herndon is quite 

 rapid, being more than 80 feet in the 20 miles. From this point its fall is naturally 

 more gradual as it passes out upon the nearly level plains, being only 36 feet to its 

 union with the waters of Fresno Slough, 36 miles farther down. 



In its course through the valley trough the descent of the river is still more 

 gradual, and in times of low water it winds along around sand bars in its bed or 

 bordering its banks. For example, the straight line from the junction of the river 

 with Fresno Slough to the head of Old River, where it separates into two channels, 

 is 87 miles in length, but the river lietween those points develops into 146 miles. 

 Its average width in this stretch is from 300 to 600 feet, and its depth from bank 

 top to bed is 12 to 18 feet. 



The river bed is usuallj- covered with clean siliceous sand, with here and there 

 an outci"opping of tenacious clay. The banks are generalh' of a tough alluvial 

 deposit, and, as usual with streams subject to floods, are slighth' higher than the 

 lands outside of them. 



The course of the river, and of each of the many sloughs which drain into it, may 

 be followed by the thick, luxuriant growth of swamp willows which lines their banks. 

 On the higher ground cottonwoods flourish, and oaks are scattered at intervals over 

 the entire district. 



As may be readilj- understood, the high, steep bluffs on either side of the upper 

 reaches of the river have offered great engineering obstacles to the diversion of water 

 for the purposes of irrigation, and but one attempt to this end (which resulted 

 in disastrous failure) has been made — that bj' the Upper San Joaquin River Canal 

 Company. 



The first feasible point along the river from which water may be easily taken for 

 irrigation without the building of a long line of canal above the irrigable district is 

 about 40 miles below Pollaskv, where the Aliso Canal diverts water from the river. 

 From this point down, on each side of the river, the high banks and the relatively 

 low plain beyond make the construction of irrigating canals easj", and it is from this 

 point on that we find in successful operation the S3'stems of canals deriving their 

 water from this river. 



THE SOILS IN THE DRAINAGE ABEA OF SAN JOAaUIN BIVEB. 



After the river leaves the mountains, as before described, the surface of the land 

 is at first interspersed with outcroppings of primitive rock. The soil is thin and 

 yields onlj' scant pasturage and is nowhere much above hardpan or bed rock. An 



