1917] VESTAL—FOOTHILLS VEGETATION 377 
western North America, but in the foothills of the Front Range in 
Colorado it is relatively very local in occurrence. It is frequent 
only on north-facing slopes and in canyons, where the snow lies 
deep and late. It grows in close stands or as scattered trees (fig. 7). 
Small trees of Juniperus scopulorum may occur infrequently in the Pseudo- 
tsuga forest; in unshaded areas with moist soil a few aspens may be found. 
Arctostaphylos and the prostrate Juniperus communis sibirica, so frequently 
associated with it, are seen as relics. The moist and sheltered slopes on which 
Pseudotsuga grows may in its stead be covered by the mesophytic grassland 
association, and many of its plants occur scattered among the conifers, such as 
Fics. 7, 8.—Fig. 7, Pseudotsuga association on a north slope; fig. 8, another 
ot, view, showing prevalence of grassland on side-slopes; trees conspicuous in 
profiles of distant slopes. 
Mertensia spp., Campanula rotundifolia, Pulsatilla hirsutissima, Saxifraga 
rhomboidea, Aster laevis, and one or two small ferns. 
e rock pine grows well in the moist habitats of the Pseudotsuga, if the 
young trees can get a start, and so the two species are commonly found in 
mixture, especially toward the top of canyon-slopes and in other less protected 
ces, Pseudotsuga can range into the habitats of the pine, where, how- 
ever, it is usually of less symmetrically spire-shaped form, and with fewer and 
uneven branches, so that the growth habit resembles that of the pine. 
POPULIS-SALIX STREAM-SIDE ASSOCIATION 
RAMALEY (12, p. 127, 14), part of the canyon forest formation; WATSON 
(25, p. 21), Populus angustifolia society; YouNG (28, pp. 330-33 
The poplars and willows of stream-sides form a nearly continuous belt in 
the wider and more open canyon-bottoms of the foothills. Populus angustifolia, 
