124 PROCEEDINGS OF WASHINGTON MEETING. 



The next paper read was entitled — 



NOTES ON THE CRYSTALLINE ROCKS OF CENTRAL TEXAS, WITH MAPS. 



BY THEODORE B. COMSTOI K. 



Remarks were made by Professor ('. R. Van Hise, to which the author 

 replied. 



The following paper was then read : 



THE CIENEGAS OF SOUTHERN CALIFORNIA. 

 BY EUGENE W. HILGABD. 



A cienega, in the parlance of the native Californian, is a limited area showing a 

 growth of water-loving plants, appearing sporadically in otherwise arid surround- 

 ings — usually hillsides or valley margins — and occasionally giving rise to flowing 

 springs. The economic importance lately attained by these cienegas as sources of 

 irrigation water by the aid of artesian borings, and some peculiarities of structure 

 upon which their occurrence in that particular region seems to depend, justify at 

 least a brief presentation of the facts to this body. 



A simple and typical case in point is presented, for instance, by San Antonio 

 creek, a stream issuing from a canon in the Sierra Madre near the town of Pomona. 

 in the San Bernardino valley, Los Angeles county. It is near the present divide 

 between the adjacent drainage basins of the San Gabriel river on the west and the 

 Santa Ana river on the east. Though a small stream, carrying only from 700 to SOD 

 miner's inches of water in summer time, it has formed in front of its exit from the 

 canon a debris cone or" fan " having a radius of seven or eight miles, of which the 

 apex, near the canon mouth, is between 400 and 500 feet above its base. On the 

 slopes of this fan, as well as near its base, there appear numerous cienegas, some 

 less than an acre in area, while others range up to twenty acres and over. In some 

 of these, large sycamore trees art' the only unusual indication amid the " bee-pas- 

 tures" of white sage, cactus and other plants characteristic of the thy mesas of the 

 south. In others there is added the willow and clumps of "tule" (cat-tail) and 

 other swamp plants. From some, springs issue naturally ; in all, shallow dug wells 

 find water; in many of them, artesian bores have been made with good success* 

 The deposits penetrated in these bores are, of course, such as may be expected in a 

 debris-fan ; but they vary so quickly and completely in wells only a short distance 

 apart as to show that the ancient portions of the fan have been formed under a 

 regime exactly like the present — namely, an alternation of very coarse deposits of 

 gravel and large cobbles such as are now carried by the si ream during the torrential 

 Hoods to which the high ranges are subject, with fine silt and even clay, which are 

 practically impervious to water. The abrupt diminution of velocity on emergence 

 from the canon results in the quick accumulation of cobble ridges or "karnes," 

 winch sometimes change the main channel, within a k'\\ hours, to a totally differ- 

 ent direction. It is obvious that in past times such changes of channel have thrown 

 the water of the creek from one drainage basin to the other ; at present it discharges 

 toward the Santa Ana basin, but unless artificially prevented there is no reason why 

 it mav not some time revert to the San Gabriel watershed. 



