REPORT OF COMMITTEE ON OBSERVATORIES 93 



part of the night, and at such times the seeing is said to go to 

 pieces. 



The San Gabriel and San Bernardino mountains trend nearly 

 east and west, and were it not for the depression between them at 

 Cajon canyon, through which the Santa Fe Railroad passes, they 

 would form a continuous range. The highest points in the San 

 Bernardino mountains, viz., San Bernardino peak (10,630 feet) 

 and San Gorgonio mountain (1 1,485 feet), are about 40 miles south- 

 east of Cajon canyon. From these high peaks this range dips 

 down toward Cajon canyon, which itself has an elevation of about 

 2, 800 feet above the sea. The main portion of the Mohave desert 

 lies north and northeast of the San Bernardino range. In the 

 vicinity of Cajon pass it has an elevation of about 3,200 feet. Over 

 the desert the air is subject to large and rapid variations of tem- 

 perature ; over the sea, only 70 miles away, it is not. The result 

 of this is a movement of the air which follows the line of least resist- 

 ance. This happens to be Cajon pass, noted in southern California 

 as a very windy place. When the winds from the desert are strong 

 they sweep violently through this pass southward toward the sea, 

 in the direction of the Santa Ana mountains, and there the Santa 

 Ana canyon affords a passage for them. It, too, is noted for its 

 winds — so much so that in this section of the State any very strong 

 wind is called a Santa Ana. An inspection of the map will show 

 Mount Wilson far to one side of this usual track of strong winds. 

 It is only when the pressure over the desert becomes so great that 

 the volume of moving air cannot be passed through the dip in the 

 range at Cajon canyon that the winds come across the mountains 

 directly and sweep over Mount Wilson from the north. 



Only a small portion of the Mohave desert lies directly north of 

 the San Gabriel range. It sometimes happens that winds originating 

 here sweep around the western end of the range through Soledad 

 pass and thence southward through La Canada. These winds 

 strike Pasadena, Mount Lowe, and Mount Wilson from the north- 

 west. The Southern Pacific Railway from Tehachapi to Los An- 

 geles passes through Soledad pass. 



The direction of the sea breeze through the San Gabriel valley is 

 of course from west to east. When it is strong and meets a lighter 

 current coming through Cajon canyon from the Mohave desert, it 

 prevails and swings the latter around the San Bernardino moun- 

 tains, and both then travel on through the San Gorgonio pass into 

 the Colorado desert. 



