274 CALIFORNIA ACADEMY OF SCIENCES. 



Cumbre de las Auros rises in high bare ridges 2000 to 

 3000 feet high, and again near Point San Pedro this same 

 ridge attains a height of 1940 feet in Mount Montara. 



The ridge which starts in at Mussel Rock, north of 

 Point San Pedro, reaches its highest point in Black 

 Mountain, and to the southeast runs out gradually into the 

 plain of Santa Clara Valley. The granite ridge which 

 rises at Point San Pedro breaks down before reaching 

 Pilarcitos Creek. 



West of the high ridge, of w^hich Mount Bache is a 

 part, is a granite ridge running from near Santa Cruz 

 nearly to Pescadero Creek. In this region considerable 

 study would be required to systematize the ridges. The 

 ridges and their narrow intervening valleys occupy a 

 region about sixty-five miles long by twenty-five wide as 

 a maximum. On the ocean side the mountains in some 

 places reach the sea; in other places they are separated 

 from the ocean by a narrow strip of flat land. From 

 Lake Merced to Mussel Rock the foothills are cut by the 

 ocean in bluffs from 200 to 700 feet in height. At Point 

 San Pedro the prominent ridge, of which Mount Montara 

 is the highest point, is cut by the ocean in bluffs from 1000 

 to 1500 feet high. Between Mussel Rock and Point San 

 Pedro occurs the nearly level Quarternary. Starting at 

 sea level at the mouths of San Pedro, Calera, Salt Lake 

 and Milagra valleys, it extends back into these valle3's and 

 northward toward Mussel Rock. In the latter direction 

 the ocean has cut a perfect section of the deposit, which 

 at the Rock is over two hundred feet thick. The surface 

 of the deposit rises gently as it recedes from the ocean. 

 From Point Montara the Quaternary extends southward 

 to Lobetus. At Spanish Town it is about two miles broad, 

 becoming narrower to the south. At Pillar Point a long 

 hill of the Merced series rises from the Quaternary, and 



