1922] Vaugkan: Geology of San Bernardino Mountains 367 



the same, except that it does not possess the evidence of strain. The 

 granite just beyond the east corner of the limestone is pale yellow in 

 color, fine-grained, and composed almost wholly of orthoclase and 

 quartz with the orthoclase predominating. No plagioclase is present 

 and only a few flakes of biotite, and this is leached to a pale green. 

 A few grains of magnetite and titanite occur, usually with the biotite. 



The rock around Chaparrosa Spring is similar to that of Granite 

 Peak. It consists of equal amounts of orthoclase and quartz with 

 biotite as principal accessory, and small amounts of muscovite. Of 

 course, being isolated from the main mass to the west, there is no way 

 really to check its identity, but it is believed to belong to the Cactus 

 period of intrusion. 



The area of granite around Fawnskin Valley extends southward 

 to Lake Creek and thence eastward beyond Elsie Caves. For the most 

 part it is the same medium-grained biotite granite so common in the 

 region, but south of Pine Lake there are several varieties, and one is 

 inclined to place them with the older masses of similar nature into 

 which the larger uniform masses of Cactus granites are included. One 

 of the most prominent varieties is a porphyritic granite which presents 

 several variations in texture. In some places the rock seems to be a 

 solid mass of large orthoclase crystals to the exclusion of ground mass 

 and there is often a tendency to a flow structure, in which case the 

 crystals in the ground mass assume a parallel arrangement, but the 

 large phenocrysts do not. 



This area extends across the canon to Martin Glen and up to San 

 Gorgonio Mountain. Along Mountain Home Creek the rocks show 

 great diversity in both composition and texture. They are true gran- 

 ites, the orthoclase content being high and the plagioclase unimport- 

 ant. All contain considerable quartz and both biotite and hornblende 

 are abundant as the ferromagnesian constituents. The texture varies 

 from medium to very coarse and in a few cases is porphyritic, some 

 of the orthoclase phenocrysts being five centimeters across. There are 

 some darker masses, probably inclusions, and the whole is crossed in 

 all directions by pegmatite dikes from an inch to two feet thick. 



Several varieties of granite are found at San Gorgonio Mountain. 

 That on the north peak is a fine-grained light pinkish grey rock con- 

 sisting of equal amounts of quartz and pink orthoclase with biotite 

 as the most prominent accessory, but it also contains considerable 

 muscovite. A small part of the quartz and orthoclase occur in micro- 

 graphic intergrowth. Only a small amount of plagioclase, oligoclase, 



