Geology from a Motor Car 361 



resulted in lowering the divide at the summit, and thus a notch 

 was cut in the mountain crest which made a "pass" possible. 

 The elevation of the Pass is 728 feet. 



Cahuenga 'Peak.; Basalt Rock in Pass 



Off to the east is Cahuenga Peak, rising to a height of 1,825 

 feet. Its western face is a fault cliff. To the west of the Pass 

 rises the rough and rugged Santa Monica Range, the core of 

 which is granitic rock. The two streams which have their 

 heads in the divide of Cahuenga Pass are on soft friable rocks 

 (of Pliocene age, Topanga formation). In the Pass will be 

 observed brownish-black rocks overlain by massive lighter col- 

 ored brown sandstone (Topanga formation) . The dark rock 

 is basalt, a volcanic rock that was forced upward in a molten 

 condition under, or between, the sandstone layers. This rock 

 was in a highly heated viscous form, the heat of which baked 

 the sandstones with which it came in contact. Alternating 

 layers of basalt and sandstone are seen, particularly in the south- 

 ern half of the Pass. Farther north the baked sandstones and 

 basalt disappear, and the formation exposed is the lighter brown 

 and fine-grained shale (Topanga formation) . The formations 

 dip toward the north and form the floor of the San Fernando 

 Valley. 



San Fernando Valley and Pass 



The San Fernando Valley is a great sunken basin, or down- 

 dropped block of the earth's crust, surrounded by mountains, 

 the floor of the basin depressed while the surrounding moun- 

 tains were uplifted along fault planes. The outlet of the Val- 

 ley is Los Angeles River, which leaves the basin through the 

 faulted valley at Burbank. Two main thoroughfares lead out 

 of the Valley to the south and east, the Cahuenga Pass and that 

 through which the Los Angeles River flows by Burbank. 

 North of San Fernando the highway crosses folded and crum- 

 pled hills, bent and folded by the upheaval by which the San 



