GEOLOGY OF BAJA CALIFORNIA. 175 



tance of 20 to 30 miles. Surmouuting this are several mi- 

 nor ranges and sharp peaks attaining an elevation of 3,000 

 to 4,000 feet. Consulting Plate II, it will be seen that on 

 the whole these latter form an interrupted series running 

 from the boundary to below Santo Tomas at a distance 

 of 10 to 15 miles from the coast. A rapid descent leads 

 from the divide of the coast range to — 



2. The interior valleys, an interrupted series of depres- 

 sions in the middle of the chain at an elevation of from 

 1,800 to 2,000 feet. 



3. The second orographic block, rising rapidly from the 

 valleys and continuing as an almost level plateau with a 

 gentle slope up to the peninsular divide, and the abrupt, 

 almost precipitous descent to the desert. The elevation of 

 this remarkable plateau is from 4,000 to 5,000 feet. 



The desert forms a sandy plain, traversed by a few lower 

 ranges, running northwesterly and southeasterly, and has 

 in general a very inconsiderable elevation. Part of this 

 plain ia doubtless depressed below the level of the sea. 



GENERAL GEOLOGY. 



According to Prof. Gabb, the characteristics of the three 

 principal divisions of the peninsula are as follows : The ex- 

 treme south is occupied by a granitic range with mica- 

 schists exposed on the northern side. The second division 

 is pre-eminently that of the mesa sandstones. For a distance 

 of over 300 miles the largest part of the peninsula is formed 

 by these. Heavy beds of generally non-fossiliferous, coarse 

 sandstones slope with a gentle dip westward from the divide 

 towards the Pacific. Towards the east the strata, during 

 the rapid descent to the Gulf, as a rule, preserve the same 

 dip. It appears as if the sandstones had been cut off by 

 a gigantic fault. A section across the peninsula would be 

 somewhat as shown in Fig. 1. 



