1905 



FORESTRY AND IRRIGATION 



79 



shown recently during the preliminary 

 reconnaissance of the Shoshone pro- 

 ject in Wyoming. At the point select- 

 ed for a dam the river had cut through 

 a deep and narrow granite canyon and 

 apparently flowed over rock of the 

 same formation. All indications were 

 that bed rock would be found at a 

 depth of ten feet maximum. On put- 

 ting a drill at work, however, it was 



it. The borings did show, however, 

 that there was 30 feet of gravel and 

 boulders underlaid with soft material 

 quick sand which would not per- 

 mit the building of a heavy structure. 

 On the Colorado River a desirable 

 site was discovered, so far as the sur- 

 face conditions indicated, where a 

 point rock stood ten feet above the 

 water surface. Two hundred feet 



North Platte River, looking upstream from Dam site at Pathfinder 



Reservoir, Wyoming. 



shown that bed rock was 88 feet below 

 the bed of the river. What looked to 

 be a thin layer of gravel proved to be 

 88 feet of gravel and slabs that had 

 fallen from the canyon walls, some of 

 these being 30 feet in thickness. 



At one diversion site on the North 

 Platte River, where conditions seemed 

 favorable for bed rock at 25 feet, bor- 

 ings to a depth of 90 feet failed to find 



away borings 120 feet below river bot- 

 tom failed to find solid foundation. 

 In a great many cases a few hundred 

 dollars expended in borings have re- 

 sulted in changing the location of dam 

 sites, and, of course, have saved many 

 thousands of dollars. 



The same conditions hold good in 

 the examination of reservoirs, where 

 natural depressions are used to store 



