GEOLOGY OF BAJA CALIFORNIA, 187 



through the northern part of the valley, as a glance at the 

 map (Plate II) will show. The two basins are separated by 

 a very low range of hills, dividing the valley in two sec- 

 tions. Emerging from deep carious in the eastern range the 

 rivers pursue a winding course through the valley to break 

 through the western or coast range in equally deep and 

 rocky gorges. To the east and west the valley is bordered 

 by steep mountain barriers. An especially steep granite es- 

 carpment runs along the western side from Ileal del Castillo 

 southward. (See Plate II.) The road from Ensenada to the 

 Real, which strikes the valley at its central east and west 

 line, descends rapidly from the summit for the first few hun- 

 dred feet over granite; the remaining two miles, till the 

 level of the valley is reached, are occupied by dark, 

 massive, more or less fine-grained dioritic rocks, which in 

 all probability should be referred to the metamorphic series. 



As soon as we reach this last-mentioned terrane very nu- 

 merous quartz veins, formerly absent or scarce, are noticed. 

 When the valley is reached the road bends northward to- 

 wards Real del Castillo, and runs over the quaternary accu- 

 mulations of debris forming the surface of the valley. The 

 low range of hills separating the northern from the southern 

 part of the valley, consists partly of granite, partly of me- 

 tamorphic slates. 



The little Mexican mining town of Real del Castillo lies 

 on the Guadaloupe River at the point where it leaves the 

 valley, and enters the rocky canons of the coast range. 

 Some placer and even quartz gold-mining has been carried 

 on here by the Mexicans for about twenty years. 



Fig. 1, Plate V, represents a profile across the northern 

 end of the valley at the Real. It will be seen that immedi- 

 ately below the steep granite escarpment to the west of the 

 town metamorphic rocks begin, at first massive and dioritic, 

 then decidedly slaty and composed mainly of chloritic 

 schists, continuing for three miles eastward across the first 

 low hills north of the valley. The strike is generally N.-S. 



