338 



University of California Publications. 



[Geology 



large as two inches in long diameter, outcrops on the north wall 

 of the Santa Ana River Valley one mile north of The Pines, 

 along the trail from Seven Oaks to Bear Valley, Sec. 5, Twp. 

 1 N, R. 1 E of the San Bernardino Base and Meridian lines. 

 San Gorgonio Mountain, the summit of the San Bernardino 

 Range, is composed of granitic rock and gneiss. 



GEANITIC BED-KOCK OF THE MOHAVE DESERT AND 

 CONTIGUOUS EANGES 

 The southern slopes of Granite Mountain, north of the wagon 

 road from Victor vi lie to Rabbit Springs, are composed of a 

 granitic rock exhibiting the exfoliation characteristic of rocks 

 of this general composition everywhere in the desert. Granitic 

 rocks are also exposed in the vicinity of the town of Victorville, 

 where the Mohave River has cut a narrows through them. They 

 also outcrop in the ranges northeast, north, and northwest of 

 Barstow, where at least a part of them are granodiorites, are 

 crossed by the Southern Pacific Railroad between Rosamond 

 and Mohave, are found in the Tehachapi Mountains west of 

 Tehachapi Pass and at the pass, in the Sierra Nevada east of 

 the pass, and east of Red Rock Canon in the southerly spur of 

 the El Paso Mountains which flank the Sierra Nevada on the 

 south. These rocks vary considerably in color, composition, and 

 texture and are cut rather commonly by pegmatite and aplite 

 dikes. 



LAVAS PERHAPS EARLIER IN AGE THAN UPPER MIOCENE 

 A lava flow of very basic andesite or of acid basalt overlies 

 granitic rock and underlies the basal beds of the Rosamond 

 Series north of Barstow. Another lava, called by Gilbert 5 an 

 "orange, massive, subspherulitic rhyolite," rests on a granitic 

 rock in Red Rock Canon, on the southern spur of the El Paso 

 Range. Lindgren describes a rhyolite, upon which the Rosa- 

 mond Series is deposited, in the Calico Mountains. These lavas 

 may belong to the general period of the Rosamond Series, 

 although their weathered and eroded surfaces indicate that they 

 are very likely older. 



" Geogr. and Geol. expl. and Surv. west of 100th merid., vol. 3, pp. 

 3 42-143, 1875. 



