E. W. HILOARD — THE CTENEGAS OF CALIFORNIA. 127 



oftheSanta Ann range. In these, as in the upper San Bernardino valley, "arte- 

 sian " springs rise at many points, and vegetation remains bright green all summer. 

 Borings thus far made have developed a very copious artesian flow, and a tunnel 

 driven through one of the clay ridges toward the cienega was suddenly inundated 

 when its face reached the gravel of the debris mass, about 40 feet below the surface. 

 The artesian wells and natural surface flow from these cienegas, so far as developed, 

 yield an aggregate flow of nearly GOD miner's inches, which can doubtless he mate- 

 rially increased; and this, with the flow from the lake above, constitutes the water 

 supply for the colonies below. 



These examples, which could be greatly multiplied, show sufficiently both the 

 nature and origin of the cienegas, and also their practical importance as sources of 

 water supply, which calls for a more careful survey of their extent of occurrence 

 than has heretofore been made. While they do not render the establishment of 

 artificial storage reservoirs superfluous, they do supplement them locally to a very 

 material extent, rendering it possible to occupy for agriculture huge areas that 

 otherwise would have remained arid for many years to come. But there arises the 

 question as to the geographic limits 'within which these natural storage reservoirs 

 may reasonably be sought, for it is notorious that they are not usually found, and 

 the name and idea of the cienega is not generally known, in the northern portions 

 of California. 



The essential condition of cienega formation is manifestly the opportunity for the 

 abundant formation of deposits of exceptionally coarse and pervious; gravel and 

 cobbles near the points where the canons emerge from the mountains. This, again, 

 is necessarily conditioned upon the occasional occurrence of violent, torrential rain- 

 fall in the mountains, alternating with periods when quiet deposition allows of the 

 formation of water-shedding layers. Another condition appears to be the ready 

 weathering of the parent rocks into rounded forms, by winch close packing is pre- 

 sented, so that abundant interspaces are permanently maintained. 



Both conditions are fulfilled to an unusual extent in the granitic ranges of south- 

 ern California. The rock is rather easily disintegrated, firsl into larger and then 

 into smaller rounded masses, from which large quantities of very coarse angular 

 sand have been detached, and which continue to disintegrate rapidly when exposed 

 to the air, but are relatively stable when submerged in the debris mass, and SO 

 maintain porosity. Such granitic or granitoid material forms the main bodyofall 

 the larger cienegas I have examined in southern California ; and the remarkably 

 large proportion of potash contained in their waters in consequence is of no small 

 economic importance. 



li is therefore reasonable to presume, and it seems d priori probable, that a 

 concurrence of the two conditions, climatic and petrographic, is requisite for the 

 formation of cienegas upon a practically useful scale ; and the extent to which this 

 concurrence actually exists, geographically, is a question of do little practical in- 

 terest. 



Professor Hilgard's paper was discussed by Professor C. K. Van Hise. 



