174 CALIFORNIA ACADEMY OF SCIENCES. 



1. The extreme south, from La Paz to Cape St. Lucas. 

 This small division apparently differs in structure from the 

 rest, and is said to be occupied by a transverse E. -W. 

 chain, not exceeding 5,000 feet in elevation. 



2. In the 300 miles of distance from La Paz to Santa Ger- 

 trudis the divide of the peninsula is placed very near the 

 eastern coast, and its elevation does not exceed 4,000 feet; 

 frequently it is not more than 3,000 feet. The eastern slope 

 is abrupt and steep, while the western is occupied by gently 

 inclined and smooth table-lands or mesas, separated by nar- 

 row, rocky canons. 



3. The northern division, from Santa Gertrudis to the 

 boundary line, is more varied in its topographic features. 

 The table-lands disappear, and a mountain chain rising in 

 the middle of the peninsula fills with its branches the whole 

 western half ; the eastern chain becomes lower and soon 

 sinks under the sands of the desert plains adjoining the 

 gulf. 



Eising rapidly, the western chain reaches an elevation 

 of 10,000 to 11,000 feet in the range of San Pedro de 

 Martis, about 120 miles south of the boundary line. From 

 here it sinks again, and runs with a maximum elevation of 

 from 5,000 to 6,000 feet up to Alta California. In the 

 section referred to and described in these notes, from Todos 

 Santos Bay eastward to the mouth of the Colorado River, a 

 distance of about 100 miles, the summit of the range runs 

 at a distance of 60 miles from the Pacific, and divides the 

 peninsula into two distinct parts — the Desert and the Pen- 

 insular Cordillera. This division applies for a distance of 

 at least 100 miles south of the boundary line. 



The topographic features of the long western slope of the 

 Cordillera are somewhat diversified, but on the whole they 

 may be divided into three sections: 



1. The coast range, or the first orographic block, rising 

 gradually from the sea to an elevation of 3,000 feet in a dis- 



