252 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



gradual amelioration of glacial conditions for several thousand years 

 (Russell, 1941, p. 86). In these latitudes this change has been mani- 

 fested by the northward spread of desert conditions. It is illustrated by 

 the progressive drying of lakes Bonneville, Lahontan, Searles, and Death 

 Valley. The Mohave River lies directly east of the Channel Islands 

 and far enough south so that the gradual elevation of the Sierra Nevada 

 could scarcely have cast a rain shadow over this region. The drying of 

 the lower streams and lakes of the Mohave system is most eloquent 

 testimony of this increasing desiccation. The study of lake varves and 

 tree rings (Huntington and Visher, 1922), and of ancient Syrian 

 civilization (Butler, 1920) all point to the same progressive desiccation 

 of these latitudes. 



Progressive desiccation of the island area itself is indicated, too, 

 by the fact that seedlings of several insular endemics, such as Lyono- 

 thamnus (Ironwood), Dendromecon (Tree Poppy), and Quercus 

 tomentella Engelm. (Island Oak), have rarely been found. A few 

 Dendromecon seedlings have been found in disturbed soil about mine 

 dumps on Santa Catalina. The lack of young plants of the above men- 

 tioned endemics may be due, in part, to grazing animals or to the com- 

 petition of exotic plants, but the evidence seems to indicate that these 

 plants are incapable of reproducing themselves at present under normal 

 climatic conditions. 



The effect of long continued desiccation would be to modify the 

 life forms of the individual species, and to produce changes in the flor- 

 istic composition of the plant communities. Direct evidence of such 

 change will be produced later in this paper. 



Climate 



The classification of the climates of the Channel Islands has been 

 an unsettled question in the past owing to the lack of adequate data. 

 However, the United States Navy has recently established two aero- 

 logical stations, one on San Nicolas in 1932, and another on San Cle- 

 mente in 1937, and the Coast Guard has been recording meteorological 

 data on Anacapa since 1934. A Weather Bureau station was established 

 at Avalon, Santa Catalina Island, in 1909, and its records have since 

 been continuous. The San Miguel Station of the Weather Bureau was 

 established in 1897, discontinued in 1903, reestablished in 1906, again 

 stopped in 1921, and resumed from 1940 to 1942. These various records, 

 when assembled with other observations to follow, enable reasonably 

 definite conclusions to be drawn. 



