148 WATER ON PLATA — CHIRICAHUI HILLS. 



It is smooth as a bowling green, without any river bed in its middle ; the small creek beds, 

 leaving the mountains on each side, only run a short distance, and lose themselves by sinking 

 in the sand in dry weather, and in the rainy season by delivering their waters into the shallow 

 lake which then occupies the playa bottom. 



On the north edge of the playa, along the trail and toward the middle of the plain, are a 

 series of pools or springs, which yield a large supply of water, which at this season was very 

 cool but exceedingly unpleasant, being slightly saline, sulphurous, and highly impregnated 

 with decaying vegetation. These springs form a boggy marsh or swamp as they flow several 

 yards along, giving growth to juncus, carrizo, and tule. These springs are included between 

 layers of clay in the alluvium, and are not derived from leakage through stratified rock. They 

 are produced by the infiltration and wash of the slope of the plain outside the playa oozing 

 up through some fissures in the clay. A large supply of water might be obtained by sinking 

 wells along this line a mile north and south. 



An effervescence of carbonate of soda and salt is found around this moist district. 



GEOLOGY OF THE CHIRICAHUI MOUNTAINS. 



The Chiricahui range is a small, well-defined mass of mountain, standing prominently out 

 from the level basin which surrounds it. The playa just described extends around its northern 

 and southern extremities, so that, though lofty and of considerable breadth, it is completely 

 isolated, and forms one of the many peculiarities of this latitude. 



Yet it preserves the trend common to all the mountain ranges here, viz: N. 40° W., and lies 

 in the line of the prolongation of the axis of the Piiialeno range, of which it may be con- 

 sidered the southern extension, that range in which lie Mountains Graham and Turnbull. 



It has also the same geological structure as the Piiialeno range. Major Emory crossed the 

 latter in two places, and found on the slope the following disposition : 



Granite, very coarse. 



Eed sandstone_, in layers one foot thick. 



Conglomerate of sandstone and pebbles. 



The depth of the two last was many hundred feet, with the stratification much deranged. 

 Near the mouth of the San Francisco the formations were : 



Granite, with much red felspar. 



Argillaceous limestone, with a west dip. 



Sandstone, calcareous and coarse grained. 



Diluvium. 



Descending the Gila toward Saddleback Peak the following order of rocks occurred : 



Granite. 



Compact limestone. 

 Black slate. 

 Eed sandstone, dip southwest 25°. 



Although tli^e limestone and granite were observed very close together, yet in no case were 

 they found in contact. 



Saddleback Peak, when viewed from a distance, appears to be made up in its upper portions 

 of limestone capped by amygdaloid, and, perhaps, composed below of sandstone, limestone, 

 and conglomerates. 



