GANNETT] EESEKVOIRS. 343 



of the canon of that river, known as Pleasant Valley. It is about 10 

 miles long by 3 in average width. The river passes through it, cutting 

 its way out through a gap but a few rods in width, having vertical 

 walls several hundreds of f^et in height. At this jjoint it could easily be 

 dammed and the water drawn off as needed by the channel of the river. 



A very favorable point for forming a large reservoir on the Eio 

 Grande is near the foot of San Luis Valley, where the river, from flow- 

 ing with a gentle current down the valley, nearly on a level with its 

 general surface, suddenly runs into a narrow passage between two per- 

 pendicular walls of basalt. A dam at this point would collect all the 

 water which the stream would annually bring down, but, owing to the 

 very flat surface of the valley, the water would spread over a great area 

 and the reservoir be proportionally shallow, and hence a large part would 

 be wasted by evaporation. 



It is unnecessary to dwell further on this subject of reservoirs, as the 

 necessity for them is far in the future. 



