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Polygala californica Lonicera Ledebourti 
Acer californicum Baccharis pilularis 
Lithraea laurina Baccharis Plummerae 
A large percentage of these species, which are chiefly confined 
to the northern part of the sub-district, are common in northern 
California. They simply reach their southern limit within this 
sub-district. In this connection the influence of the Santa Monica 
Mountains should not be passed by unnoticed. This cross range, 
although seldom reaching a higher altitude than 750 meters, exerts 
a marked influence on the northern and southern distribution of 
plants along the coast. The two oaks, Quercus lobata and Quercus 
Engelmannii, are notable examples of species that are checked by 
this range in their northerly or southerly distribution. Several 
northern shrubs, such as Myrica californica and Baccharis pilu- 
laris, do not occur south of this range. 
The Interior Sub-district occupies the foothills and the 
typical chaparral of the interior mountains which are shut off 
from the direct influence of the sea-breeze by hills or low moun- 
tains. The western boundary is outlined by the Coastal Sub- 
district, and its inland by the Transition Zone of the higher 
mountains, or by the deserts in the lower mountains and passes. 
This sub-district extends from the Liebre Mountains southeast- 
ward along the coastal slope of the San Gabriel, the San Bernardino, 
the San Jacinto, and the Cuiamaca mountains. 
The chaparral, of which the sub-district is almost wholly com- 
posed, is separated into several altitudinal belts. These alti- 
tudinal floral changes are very evident to one ascending any of 
the mountain trails. Along the base of the mountains, sometimes 
extending up their slopes several hundred feet and out over the 
footslopes, is a belt intermediate between the Upper and Lower 
Sonoran. Here the prevailing plants are Ramona stachioides, 
Eriogonum fasciculatum foliolosum and Senecio Douglasit. Ascend- 
ing the steep mountain slopes one passes into the typical chaparral. 
Adenostoma fasciculatum prevails through the lower altitudes in 
the eastern part of the San Gabriel Mountains, and in the San 
Bernardino andt he San Jacinto Mountains, but on the Mount 
Wilson trail, which is intermediate between the Coastal and the 
Interior Sub-districts, Quercus dumosa and Ceanothus crassifolius 
are the predominating species. Further up the slopes these species 
gradually give way to others, of which Ceanothus divaricatus 
