GEOLOGY OF CARRIZO MOUNTAIN, CALIFORNIA 



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predominant. Fairbanks reports that the limestones constitute the 

 mass of the north face of the mountain. They are likewise present 

 in great force on the divide between Alverson and Garnet canyons, 

 where bands of graphitic schists are associated with them, but south- 

 west along the first-named canyon, bands of dark biotite gneiss, 

 which presumably represent early intrusives in the limestone, are 

 abundant. Other fresh, dark, fine-grained intrusives, which may be 

 related to the Miocene effusives, are found in narrow dikes. 



Fig. 3. — Alverson Canyon and the west slope of Carrizo Mountain. 



The bedding of the marmorized limestones and the imperfect 

 foliation in the gneisses are approximately parallel to each other and 

 to the longer axis of Carrizo Mountain. They usually are nearly 

 vertical, the dips in either direction being 70 or 80 degrees. 



The basement of Black Mountain was observed at only a few points 

 where the fundamental rock juts out into Barrett Canyon. Here it 

 is a granitic plutonic, with little or no evidence of the action of meta- 

 morphic forces. Fairbanks, who examined it at a point somewhat 

 farther east, also speaks of the rock as a granite. 



Effusives. — West of Alverson Canyon (Fig. 3), along the north 

 slope of Carrizo Mountain, is a conspicuous exposure of ashy, laven- 



