354 



University of California Publications. 



[Geology 



in the flows. On the hill north of and above the first stamp mill 

 west of the Southern Pacific track, and northwest of Rosamond 

 station, is a red porphyritic lava with phenocrysts of quartz or 

 sanidine and subordinately feldspar. In places this lava is also 

 felsitic with flow structure and contains some light gray perlite. 



At the northeastern end of that portion of the Rosamond 

 exposure west of the Southern Pacific tracks is a fault with 

 splendid examples of slickensiding. The beds here contain agate, 

 chalcedony, opal, silicified wood and a considerable amount of 

 bedded chert. About one-eighth of a mile farther west is a thin 

 bed of highly vesicular basalt probably of not very great hori- 

 zontal extent. Immediately over this basalt is a thin layer of 

 green, rose, and brown agate, in which the green is interwoven 

 with the other colors in very complex patterns. Amygdules of 

 quartz, with crystals sometimes forming a comb-structure in the 

 centers of the cavities, occur in vesicles and cavities of the basalt. 



THE EOSAMOND SEEIES IN EED EOCK CAnON 



The mouth of Red Rock Canon is about twenty-five miles by 

 rail north of the town of Mohave. The canon drains a portion of 

 the southern slope of the Sierra Nevada and just above its mouth 

 cuts through a southwestern spur of the subsidiary El Paso 

 Range. The Rosamond strata, which outcrop in Red Rock Canon 

 on both sides of this spur, were first described by Gilbert, 12 whose 

 original account is here quoted in full: 



In the vicinity of Walker's Pass there is a long, low, detrital slope 

 from the Sierra Nevada to the desert at the east, and the same exists 

 thirty miles farther south. In the interval the slope is interrupted by 

 the low, irregular El Paso Mountains, which appear to have risen, in 

 part at least, since the establishment of the detrital slope. Bed Eock 

 Canon, having a southeast course, intersects a southerly spur of the 

 El Paso Mountains, and rises among detrital beds that lie between this 

 spur and the Sierra Nevada. For two or three miles it cuts obliquely a 

 series of beds dipping westward from the El Paso spur, at angles ranging 

 from 15° to 30°. Pig. 56 gives a section normal to the strike, but based 

 on notes taken along the oblique cutting of the canon. No. 1 is a lightly 

 cemented coarse sand or fine gravel, pale umber to ochre in color, and 

 consisting of rounded grains of quartz, mica, feldspar, and divers vol- 

 canic rocks. Upward it is inseparable from the granite sand of the 



is Geogr. and Geol. Expl. and Surv. W 100th Merid., vol. Ill, pp. 142 

 and 143, 1875. 



