GEOLOGY OF BAJA CALIFORNIA. 193 



That this patch of auriferous gravel has been formed by 

 an ancient river of considerable importance is certain, but 

 the most interesting questions are, whence did it come and 

 to where did it flow, and where are the metamorphic rocks 

 that furnished the material for the boulders? I saw no 

 granite pebbles; if there are any they are very few or have 

 been destroyed by weathering. It will be observed that the 

 granite disintegrates very easily, and that the present rivers 

 running through San Rafael valley carry mostly sand and 

 but little pebbles. It was not possible to determine the 

 direction of the fall as the bed rock is not exposed, but it 

 is probable that the general course of the river was east 

 and west. If so, where did it head if flowing west, or 

 where did it go to if flowing east ? The great escarpment 

 of the range is but few miles distant. I was informed that 

 at Camp Juarez, about 20 miles north of Campo Nacional, 

 there are similar deposits; the gold from the two places is 

 certainly identical. I was also told that still further north, 

 but further down the west slope there is a similar hill near 

 Vallecitos. Finally Mr. R. Stevens informs me that the 

 plateau near Santa Catarina is capped with a reddish 

 "cement," which maybe a volcanic formation or a gravel 

 deposit. Nothing detiaite can be said of the age of these 

 auriferous gravels except that they certainly date from a 

 time when the drainage and the whole topography of the 

 peninsula were very difterent from what they are now. They 

 may be tertiary and equivalent to the auriferous gravels of 

 the Sierra Nevada. At any rate, they show conclusively 

 that the present plateau is part of a very old continental 

 area . 



Of the desert and the desert ranges near the Colorado 

 river I have but little to say as I did not visit them. I 

 have sketched in the great Salt Lake and the ranges beyond, 

 from the view obtained from the great escarpment. 



These mountains of the desert are about 2,000 feet high, 

 and apparently predominantly composed' of granite on 



