RYDBERG: VEGETATIVE LIFE ZONES OF ROCKY MOUNTAINS 485 



The foothills are far from uniform, depending partly on the 

 region on which they border; those of the eastern slope are very 

 different from those of the western, those in the south different 

 from those in the north. In the foothills are included both the 

 lower mountains of the Rockies, the high mesas and plateaus often 

 bordering on the same, and the Isolated mountains, hills, and 

 bluffs in the neighboring region. 



I . Foothills of the eastern slope of the Northern Rockies 

 The foothills are here usually covered with scattered growth of 

 Bull Pine, Finns scopulorum, and on the steeper hillsides by 

 Sahina scopulorum, and to a great extent covered with the common 

 grasses and other herbs of the plains. In the upper portion of 

 the hills, F seudotsiiga mucronata and other trees of the Montane 

 Zone are often found in the valleys. The river bluff and hill- 

 sides with richer soil are covered by groves of Frunus melanocarpa, 

 Grossularia setosa, Ribes odoratum, R. inebrians, Acer Douglasii, 

 Rhus trilobata, Symphoricarpos occidentalis, Amelanchier alnifolia, 

 and related species. In the canyons and valleys are groves of 

 Fopiilus angustifolia, F. Sargentii, F. acuminata, some willows and 

 birches, Negmido interior, and In the drier part of the same Frtmus 

 americana and several species of Crataegus. Many of these trees 

 and shrubs really belong to the flora of the Plains or even to 

 prairie-division of the Upper Austral Zone, and have followed the 

 rivers up. In the Black Hills of South Dakota and In some of 

 the hills and ridges In western Nebraska to these are added, 

 Quercus macrocarpa, Ostrya virginica, Celtis occidentalis and C. 

 crass if olia, Ulmus americana, Fraxinus campestris, and Cercocarpus 

 montanus, all except the last belonging to the eastern flora. The 

 lower hills, as well as tablelands and flats, are often covered by 

 sage brush, principally Artemisia tridentata and A. cana, and 

 rabbit brush, I. e., various species of Chrysothamnus. 



Although the foothill region in central Montana covers large 

 areas, the zone is really rather narrow In altitude and becomes 

 still narrower further north. As far as I can understand, it has 

 disappeared in the Canadian Rockies. At least, the hills sparingly 

 covered by Finus scopulorum so characteristic of the belt in 

 Montana, northern Wyoming, and western Nebraska are not 

 there. Even the tree itself seems to be lacking north of latitude 



