78 R. W. Chancy 



and stems of Nuphar and Typha, together with grasses and 

 sedges, give a picture not unlike that in many arid and semiarid 

 parts of Asia and North America today, where low precipitation 

 and the consequent reduction in importance of valley develop- 

 ment result in the presence of numerous shallow basins at the 

 foot of mountain ranges. 



Although the Pliocene floras of both continents show a 

 marked resemblance to the modern vegetation of the same 

 regions, there is apparent in most of them a somewhat less arid 

 aspect than exists at present. The physical conditions character- 

 izing this epoch may be summarized as having involved a 

 topography essentially as diverse as that of today, together with 

 a climate in which high range of temperature and annual rain- 

 fall varying from lo to 20 inches resulted in the development of 

 locally differentiated plant formations with relatively few generic 

 and specific representatives. 



The Pleistocene floras of western America have been so re- 

 cently and adequately described by Mason and others'^' 

 that the present discussion warrants only a brief summary of 

 the plant record for the epoch immediately preceding the Recent. 

 Most of these floras represent coastal vegetation in California 

 that is of essentially the same type as that now living, including 

 a large number of herbaceous species represented mosdy by 

 fruiting structures. The most significant difference in the present 

 discussion is that certain of the Pleistocene florules, notably those 

 from Carpinteria and Santa Cruz Island, are made up of species 

 which occupied regions several hundred miles beyond the pres- 

 ent southern limits of their range. The extension into southern 

 California of the range of such species as Cupressus goveniana, 

 Pinus radiata, Pseudotsuga taxifolia, and Sequoia sempervirens 

 may be interpreted as an indication of increased precipitation 



