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sisten t decline in hydrostatic head, is less than the recharge fa cto r, there is no immediate cause fo r alarm that present sources, properly developed and expanded, woiild be unable to economically supply the m unicipality’ s demand fo r a long period. Hydrostatic declines, however, are the primary warnings that the artesian supply of the Valley has its lim itations; therefore, alert measures fo r its conservation should be constantly observed. "Map No, 1 (copy o f which I w ill pass around for your review) outlines the water shed of Las Vegas Valley, and a ll water which eventually may issue as springs or be produced from wells has been precipitated as rain or snow within the boundary of the area outlined. As a study of the structural history o f Las Vegas Valley was a necessary preliminary to the determination of hydrologic conditions, a b r ie f review of this history is worth while, as there is a d irect relationship between the geology of the Valley and its water resources, "Las Ve gas V alley, and the mountains which form its peri­phery, is an example of the Basin-Range "type o f structure in which the pre­dominant feature is that of a mosaic of fa u lt blocks. Elevated blocks con­stitu te the present mountain ranges, while depressed blocks or the lower portions of t ilte d blocks outline the va lley s. These valleys often become closed, doubtless partly due to detritus resulting from erosion, and in the case of Las Vegas Valley by lava flows in its lower portion. A lake at least 80 miles in length once occupied the flo o r o f the v a lley , and therein was deposited sediments consisting principally of clays, fin e s ilt s , and fresh­water limestones. At intervals torren tia l storms swept gravels and sands fa r out into the lake. These coarse materials become fin e r toward the center of the basin, and form ideal conduits or aquifers in which waters are now confined. Map No, 2 (I pass copy o f this map fo r your review) illu s ­trates a hypothetical cross-section of the va lley, and shows ideal conditions under which artesian flow may be encountered. "The periphery of the va lley was studied fo r the purpose of subsequently being able to deal with demonstrable data, and at this date one can state with certainty that any p o ssib ility of water flowing into the valley through under-ground channels from lakes to the north, or from the Sierra Nevada, is without foundation of fa c t. The watershed of Las Vegas Valley is the primary source, and although a major part of the precipitation is irretrieva bly lo st by run-off and evaporation, a small part finds its way way into porous strata which constitute zones in the old lake deposits, and this water alone creates the inventory which may be tapped and put to bene­f i c i a l use. "S ta tistics are available fo r average ra in fa ll at Las Vegas, and although the records are not continuous it appears that a figure of 4.88 inches annually would be fa ir ly accurate (Nevada Agricultural Experi­mental S tation ). N o ra in fa ll stations are maintained at elevations other than at Las Ve gas, consequently this figure is not usable fo r the watershed as a whole. Some research has been conducted in the eastern part of Nevada, and as a result o f these published data a ra tio of increase equal to 0.45 inch per 100 fe e t o f elevation above 2000 fe e t has been used in calculating tota l precipitation fofr the watershed* Accurate data as to recharge fa ctor would be possible only a fter a protracted schedule of observation, including weiring of a ll run-off waters and the determination o f evaporation and trans­piration fa cto rs. The p ra ctica b ility o f pursuing such a study is necessarily limited by the use to which such information could be out i t fin a l conclusions (2)