EVIDENCE OF LIMITED RAINFALL ON THl': PLATEAU. 151 



silicioua sand. From the character of the vegetation on the slope, it is evident but little water 

 is retained there, and no creek carries its bed sufficiently far to deliver its waters into the Sauz 

 stream. The rain water absorbed into the soil probably finds its way to the lower level of tlie 

 valley near the river bed, and may go to form the water pools existing there in dry seasons. 



Although no rock was observed here in place overlying the limestone, yet the dej^th of 

 detritus and gravel on the upper edge of the plain leads to the suspicion that a sandstone rock 

 is the immediate basis rock ; the reddish silicious sand also presujiposes that it is a reddish 

 sandstone, such as is found further east. 



Looking back at Chiricahui from the Sauz brook it appears a much larger range than when 

 seen from the playa. The eastern and southern j^rolongation of the mountain is only visible 

 from the Saiiz valley, where it appears to run 30 miles south of the canon. The highest peaks 

 of the mountain also lie to the south of the Puerto, and attain an elevation of 6,000 feet above 

 the sea, or 2,000 feet over the plain on either side. At such an elevation this great mass of 

 rock must attract the rain clouds of summer and receive a large supply of water ; from Septem- 

 ber to April its summits must be frequently capped with snow, thus increasing the water supply. 

 Still, it may be asked, what becomes of this water? is it all confined within the valleys of the 

 range? The arroyo beds, which are numerous and some of them deep, leading from the flanks 

 of the hill, flow one, two, or it may be even three miles into the plain, but, sooner or later, 

 they ultimately lose themselves in tlie detritus of tlie valley ; and of the few arroyos which drain 

 out from the interior of the mountain into the external plain, not one of them flows permanently. 

 There is not, in fact, comprised within the whole mountain region or its confines, one single 

 permanently flowing stream. Tlie stream beds show that occasional flows of water occur from 

 excessive rain or from unusual thaws of snow, and that from their sudden rise the waters exert 

 ^ great force in scooping out a channel ; but this only exists for, at most, a few weeks in the 

 year, and thenceforth diminish, so that for three-fourths of the year they are represented by dry 

 beds. From the apparent condition of the surface, we must conclude, notwithstanding the lofty 

 elevation of the basal jjlain and tlie mountain ranges, that but a small amount of rain falls in 

 tlie year, and that the solar evaporation must be very nearly equal to that rain fall, whatever 

 its amount ; for, if not, the plains would become water soaked from having no good surface 

 drainage, and would produce a varied and abundant vegetation. 



