220 UNDERGROUND WATERS. 



that any ot it came from the great mountains of the interior. On the 

 contrary the sand and gravel it contains are so full of porphory, finer 

 sandstones and shales that it is certain that it did not come from the 

 granite ranges on the east. It has also penetrated the interior as far 

 as Redlands where a vast bank of it underlies the present top soil of 

 that pla,ce. This seems a continuation of the Puente hills which are 

 found about Pomona traceable again at Colton, south of Redlands, it 

 crosses San Timateo Canyon and runs nto the grey hills of lime shales 

 that lie on the northern edge of San Jacinto. 



Commencing far in Lower California, a range of porphory rises a 

 few miles from the coast, crossing the line at San Isidro, and forming 

 the ledge on which the Otay Dam is built, doing the same for the 

 Sweetwater Dam and the La Mesa Dam of the San Diego Flume Com- 

 pany, crossing the lower edge of Escondido, and continuing on through 

 Santa Margarite, forming the great backbone of the hills between 

 Santa Ana and San Jacinto and sinking at Santa Ana Canyon. Where 

 the conglomerate laps upon this in the upper part of Santiago Canyon, 

 the uplift of many miles of it shows plainly that the conglomerate was 

 formed before the porphory rose. In parts of San Diego county it is 

 just as plain that the conglomerate was washed in afterward and lies 

 in position against the slopes of the porphory. 



These formations and the various layers itself compose all the geo- 

 logical features of that portion of Southern California west of the 

 desert. 



Now it is certain from many borings that old water channels lie 

 beneath this immense wash from the west and that the streams once 

 ran beneath where we now see nothing but hills. The water that sup- 

 plies the artesian wells between Whittier and Fullerton on the dry 

 mesa never comes from the local watershed of those low hills back of 

 the mesa. The Santa Ana, the San Gabriel or the Los Angeles rivers — 

 (perhaps all three of them) — in some distant day had one or more 

 channels running over a broad valley that is now covered by those 

 hills. That wash turned the main body of the stream but the gravel 

 of the old channels still continued to carry water. 



It is almost equally certain that water from the Santa Clara River 

 enters San Fernando Valley under the range of tertiary in which the 

 Southern Pacific tunnel is built. A little to the west of the tunnel 

 the granite begins, but from there west the hills are all wash. And 

 there is more water at the head of San Fernando than the local water- 

 shed can reasonably explain. 



