76 R' W. Chancy 



given it its mild, moist climate; as a result, the redwood and 

 related coniferous forests became confined to the coastal slopes. 

 From eastern Washington and Oregon the more mesophytic 

 elements of the vegetation have gradually been eliminated until 

 they survive only to a limited degree at higher altitudes in pro- 

 tected situations, with Artemisia and Juniper us occupying the 

 broad expanse of the Great Basin. 



The gradual steps by which the humid forest was restricted, 

 not only in North America but also in Asia, are being made 

 known by studies of Pliocene floras on both sides of the Pacific. 

 With the breaking up of the extensive areal units by mountain- 

 making, with resultant diversity in topography and climate, the 

 situations in which plant remains might be preserved became 

 fewer. As a result, the floral record of this latest epoch of the 

 Tertiary is less completely known than the record of those pre- 

 viously discussed. In western America, Pliocene floras are known 

 only from California and Nevada.'"' ""' '' Except in the coastal 

 region, where a modified redwood forest has persisted down to 

 the present, they are made up, in large part, of trees such as 

 Alnus, Platanus, Populus, Quercus (evergreen-oak types), and 

 Salix, which occupy stream borders in regions of low rainfall. 

 Another element, com^nsmg Arctostaphylos, Ceanothus, Cerco- 

 carpus, Garry a, and Heteromeles, makes up the first unit of true 

 chaparral that has been recognized in the fossil record. A 

 third element, apparendy confined to higher altitudes, includes 

 Cupressus, Libocedrus, Pinus (nut-pine type), Quercus, and 

 Robinia, with the palm, Washingtonia, on the adjacent sand 

 washes. Most of these Pliocene species are not only similar in leaf 

 character to modern species of their genera, but they also appear 

 to have occupied essentially the same habitats over the same 

 range. The exotic element, unlike that of older Tertiary floras, 



