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University of California Publications in Geology [Vol. 13 



recent stream cutting exposes twenty feet of alluvium, and in Pine 

 Valley, several miles to the east, there is at least fifteen feet. Similar 

 material underlies Green Valley and the small valley northeast of 

 Wynola. 



The present-day streams, both those flowing to the Pacific Ocean 

 and to the Salton Sea, are engaged in removing this alluvium. They 

 have cut channels with flat, gravel-strewn floors and steep walls to a 

 depth of ten to twenty-five feet. 



The valley now occupied by Cuyamaca Reservoir is probably also 

 underlain by alluvium and small patches of bedded alluvium can be 

 seen at various places along even the narrowest of the canons to the 

 west of the summit valleys. 



The alluvium of Pine Valley carries frequent thin layers of de- 

 composed vegetable material, separated by layers of fairly clean sand. 

 It is therefore thought that most of these unconsolidated bedded de- 

 posits were accumulated in meadows, which from time to time had 

 their grass cover buried under layers of sand. 



The Julian Schist Series 



Bodies of schistose rock inclosed in granite are of frequent occur- 

 rence in the mountains of San Diego County and have also been de- 

 scribed from Lower California. Such schists are particularly abun- 

 dant in the Cuyamaca region and form the country rock for most of 

 the gold quartz veins of the Julian and neighboring mining districts. 



The most prominent body of schist in the region extends without 

 a break from north of Wynola, through Julian, to the region of Rat- 

 tlesnake Valley, a distance of over twelve miles. Its width varies from 

 three-quarters of a mile to a mile and a half. This belt of schist will 

 hereafter be termed the main Julian schist body. 



Numerous smaller masses of schist outcrop to the southwest of the 

 main body and several outlying masses are found on its northeast side. 



Fissile quartz-mica-schist . — The central portion of the main body 

 of the Julian schist, extending from three miles northwest of the town 

 of Julian, southeastward to the limits of the area mapped, is a fine- 

 grained, fissile quartz-mica schist. A typical specimen of this rock 

 has fine-grained, blue-gray layers of quartz and sericite about one- 

 sixteenth inch in thickness, with coarser layers of quartz and biotite. 

 The quartz-sericite layers have flakes of biotite which are generally 

 not oriented parallel to the schistosity. 



