GROUND WATER. 107 



OUTCROPPING WATER ZONES. 



Previous to the discovery of the water in some of the shafts described the entire 

 water supply of the town of Tonopah was obtained from wells 4 miles to the 

 north, where geologic and topographic conditions are similar to those at Tonopah. 

 Here, in a distance of a half mile or more, along a small east-west valley, are a 

 number of wells, most of which reach water within 30 to 40 feet of the surface. 

 The wells are in solid later andesite, and the water circulates along a fractured 

 (probably faulted) zone. The trend of the water zone corresponds with that of 

 the valley, which has probably been eroded along this belt of fractures. 



These water zones can often be recognized at the surface by the presence of 

 taller and greener vegetation or by plants requiring so much water that they 

 would not thrive under the usual arid conditions. 



DISTRIBUTION AND EXPLANATION OF WATER ZONES. 



The above data show that while some of the Tonopah shafts have reached 

 depths of over 1,000 feet (in the case of the Desert Queen over 1,100) no general 

 body of ground water has been encountered, though the rocks are extremely 

 fractured; yet along certain steeply inclined fracture zones water is found 

 sometimes quite near the surface and occasionally in considerable quantity. This 

 water is cool, is sufficiently nonmineral to be fair drinking water, and is 

 undoubtedly the storage of precipitation. 



These water zones appear to be widely spaced. They have been noted only 

 in rigid and brittle rock rhyolite and andesite. They seem to occur especially 

 along intrusive contacts, where one rock has been shattered by the intrusion of 

 another. They are often, perhaps usually, accompanied by a clayey state of the 

 decomposed rock. This decomposed rock, while itself undoubtedly due to the 

 waters, now forms an impervious bottom or foot wall of the fractured zone and 

 keeps these waters from penetrating the underlying dry and fractured rocks. 

 Thus the water channel or basin has a dike-like shape. It appears probable that 

 similar clays may limit these water basins in depth, limiting the downward extent 

 of the zone-shaped basins, and thus explain why they are found sometimes so near 

 the surface in a region apparently without universal ground water. 



USUAL ABSORPTION OF PRECIPITATION BY ROCKS. 



In the southern half of the area shown on the Tonopah map (PI. XI), in the 

 depressed area capped by volcanic breccias, no water has been encountered, even in 

 shafts over 700 feet deep, although some shafts, as the Ohio Tonopah for instance, 

 have passed through the soft breccia to a rigid and fractured rock below. 

 Furthermore, in the breccia-covered region to the south, the writer does not 



