278 CALIFORNIA ACADEMY OF SCIENCES. 



forms the valley of San Francisquito Creek, finally ending 

 in Coal Mine Caiion in the flank of the Black Mounain. 



The next salient topographic feature is the main ridge 

 of the mountains. This starts at Mussel Rock and fol- 

 lows the same general direction, nearly southeast. At its 

 northern end it can hardly be distinguished topographic- 

 ally from the foothills previously described; but near 

 San Andreas Lake, it reached a height of 1300 feet and 

 is distinctly marked off by the valley just described. In 

 width it extends here from the Crystal Springs Valley to 

 Pilarcitos Valley. Its northwestern end is serrated by the 

 San Pedro, Calera, Salt Lake, Milagra and other valleys 

 into a number of long projecting points running down to 

 or nearly to the shore. Near San Andreas Lake this 

 main ridge is somewhat broken by San Mateo Creek, 

 and, after being much reduced between San Mateo Creek 

 and Pilarcitos Lake, rises and continues southeastwards 

 with very even crest as far as the San Mateo-Spanish 

 Town road. South of this road it becomes higher, with 

 narrow, slightly uneven crest, until it swings around the 

 head of the long valley described, and joins Black Mount- 

 ain. 



The end of another ridge is met near Point San Pedro. 

 This ridge, largely of granite, rises abruptly from the 

 ocean at Point San Pedro, quickly attaining a height of 

 1940 feet in Mount Montara. Continuing southeastward, 

 where it is known as the Cumbre de las Auros, it rises 

 into bare, precipitous ridges, which break down before 

 reaching the San Mateo-Spanish Town road. 



On the ocean side of this ridge and the main ridge de- 

 scribed in the preceding paragraph, high, irregular ridges 

 extend seaward between the streams shown on the sketch- 

 map. These end more or less abruptly, or else run out 

 at the coast line or a short distance inland. 



