Geol.— Vol. I.] SMITH— SANTA C AT ALT N A ISLAND. 5 



and its greatest elevation is about twenty feet. At either 

 end of the isthmus the hills rise very abruptly to the main 

 ridge, which is here from 800 to 900 feet in height. West 

 of this point the ridge has two divisions, which unite, less 

 than a mile and a half beyond, to form again a single ridge, 

 continuing to the end of the island. On this end the ridge 

 lies nearer the south than the north shore. One noticeable 

 feature of this main watershed is the general uniformity of 

 its height. For the greater part of its length the variations 

 in altitude are not more than two or three hundred feet, the 

 average elevation being about 1,400 feet. The two greatest 

 elevations are near the center of the island, the peak known 

 as "Orizaba" (or " Brush Mountain "), marked 2,109 feet 

 on the map, and " Black Jack," the peak about a mile to 

 the northeast of this, about a hundred feet lower. 



Types of Topography. — The general character of the 

 topography is very bold and rugged, and shows an advanced 

 stage of development. A general view of the island from 

 almost any point gives an impression of a close succession 

 of sharp, steep ridges and V-shaped canons. One of the 

 most marked examples of this effect is in the slopes of 

 Avalon Canon, particularly on the west side, when seen 

 from the opposite summits. 



Viewed in detail, the island shows two prevailing forms 

 of topographic relief: (i) the sharp ridges and V-shaped 

 canons just referred to, and (2) the rounded and level forms 

 belonging to an older topography. The slope of the cafion 

 walls, in the first type, is usually steep, occasionally having 

 an angle of 40° or over. The first form is the prevailing 

 one in most parts of the island, masking the remnants of the 

 second. 



The second type of topography is strongly contrasted 

 with the first. It is found in the higher parts of the island, 

 best developed in the eastern end. It is shown in the level 

 character of the main ridge, and of several of the minor 

 ridges which approximate it in altitude. These latter are 

 (i) the principal ridges between Middle Ranch Canon and 



