336 HANNIBAL: A PLIOCENE FLORA FROM CALIFORNIA 
Sequoia sempervirens (Lamb.) Endlicher. (PLATE 15, FIG. 3.) 
Redwood. 
The characteristic species of the fog or redwood belt of the 
Coast Ranges. California~-Oregon boundary to Monterey County, 
California. 
SALICACEAE 
Salix laevigata Bebb. Bebb willow. 
Occurs along streams, its zonal distribution being determined 
by stored water rather than by rainfall. Siskiyou County, Cali- 
fornia, to northern Lower California. 
Salix fluviatilis Nuttall. Long-leaf willow. 
The resemblance of the leaf parts of S. exigua, S. argophylla, and 
S. fluviatilis renders it impossible to decide which of the three the 
series at hand should be referred to. It is not generally agreed 
that the several members of the fluviatilis group represent more 
than a single polymorphic species. 
Sand bars along valley streams. British Columbia, Mackenzie 
Basin, and southeastern Canada south to Lower California, 
northern Mexico, and the District of Columbia. 
Populus trichocarpa Torrey and Gray. Black cottonwood. 
- Several of the specimens show the characteristic anastomosing 
venation and cordate bases of leaves from young shoots. 
Along foothill streams in moist situations, usually with Acer 
californicum and Fraxinus oregona in central and northern Cali- 
fornia. Occurs from southern Alaska east to Montana and south 
to San Diego County, California. 
BETULACEAE 
Alnus rhombifolia Nuttall. (PLATE 15, FIG. 6.) White alder. 
Occurs along foothill and low mountain streams. Eastern 
Washington and Idaho south to San Diego County, California. 
FAGACEAE 
Pasania densiflora (Hook. & Arn.) Oerst. (PLATE 15, FIG. 8.) 
Tanbark oak. 
The venation of this species is unmistakable. 
Characteristic of the yellow pine and fog belt, but extending 
