GEOLOGY OF BAJA CALIFORNIA. 191 



what west of north. Far to the south it is seen capped 

 with flat-topped tables. As far as can be seen the granite 

 extends; it forms the whole descent except near the desert 

 where a narrow belt of a reddish rock is seen, connecting 

 southward with dark, basaltic tables covering the desert at 

 the foot of the escarpment. Many little ridges and isolated, 

 low volcanic hills dot the desert in a southeasterly direc- 

 tion. If there is any metamorphic slate at all at the base 

 of the range, it can be but a very narrow belt. The extent 

 of the remarkable plateau forming the summit of the range, 

 must be very great. To judge from statements of reliable 

 persons this enormous granite mesa extends from near the 

 boundary to a point fifty miles south of the profile near 

 the old mission of Santa Catarina. At this place, Mr. K. 

 Stevens, who has examined that country for a proposed 

 railroad, informs me the gently sloping mesa, composed of 

 granite, reaches 5,000 feet at the summit, while the passes 

 are eroded deeper, and are at an elevation of about 4,000 feet. 

 An abrupt escarpment, equally steep as at the place crossed 

 by the profile, leads down to the desert plain, here some- 

 what higher, having at the base of the clitf an eleva- 

 tion of 2,000 feet. South of Santa Catarina, a deep valley, 

 "Valle de la Trinidad," has cut far into the mesa; south of 

 this the topography and geology are but very little known. 



We would thus have a continuous predominantly granitic 

 plateau bordering on the desert, twenty to forty miles broad 

 and extending about 80 miles southward from the boundary. 

 The descent is more or less gradual on the western side, 

 while towards the east there is an exceedingly steep slope 

 to the desert. On no map, as far as I am aware, has this 

 remarkable topographic feature been properly or even 

 approximate!}" indicated. On the general map (Plate II) 

 an attempt has been made to represent the great eastern es- 

 carpment. The map is based on the larger map of the coast 

 line of Baja-California, as surveyed by the " Narragansett " 

 in 1873; the interior topography is derived from my own 



