Smith.] 



Islands of Southern California. 



191 



(In support of this view it may be mentioned that a patch of loose, 

 water-worn pebbles was observed at one point on the main ridge 

 near the eastern end of the island.) The summits over the larger 

 part of the island were planed away, leaving a small and nearly 

 centrally situated nucleus, now shown in the two prominent peaks 

 a little to the east of the center of the main division of the island. 



Some of the canyons furnish further evidence as to the later 

 movements of the island. The rugged topographic forms of Santa 

 Catalina are, without doubt, of the same age as the coastal forms, 

 that is, mainly belonging to the post-Miocene interval of erosion. 

 In a number of the canyons deposits were formed which have been 

 cut into by the present streams. One of these canyons is a tribu- 

 tary of Avalon Canyon, having a length of about one and one-half 

 miles, with a fall in the stream bed of about 1 ,300 feet in that dis- 

 tance, thus giving a steep-graded stream, and for the greater part 

 of its length, a narrow, V-shaped canyon. Up to an altitude of 250 

 feet (as far as it was followed by the writer) the stream has been 

 cutting through earlier deposits to a depth varying from three to 

 eight feet. How much higher the same thing may be found, is not 

 known. Between the altitudes of 150 feet and 175 feet the deposits 

 had a width of about forty feet at the surface (in the narrow, V- 

 shaped canyon), and a maximum thickness of about eight feet. In 

 the center of this deposit the present stream had made a narrow cut 

 several yards in width, and, at most points, down to bed-rock. 

 Practically no impression had been made on the underlying rocks, 

 thus indicating the short time that the stream has been cutting 

 since the deposits were laid down. The rocks do not vary greatly 

 in character for the entire length of the stream course, and, so far 

 as known, there has been no barrier to cause deposits in the bed of 

 the channel. The only satisfactory explanation, therefore, is that 

 of depression since the canyon was cut, followed by elevation caus- 

 ing renewed cutting. This later elevation was prior to the depres- 

 sion which caused the drowning of Avalon Canyon at its mouth. 



In another V-shaped canyon, in the Little Harbor region, at an 

 altitude of several hundred feet, the present stream has cut through 

 an earlier stream deposit to a depth of about twenty-five feet. At 

 two other points in this same region, but in the broader parts of 



