1910] ROBBINS—VEGETATION IN COLORADO 279 
common. Sage plains stretch from the streams to the foothills; 
associated with the sage is Sarcobatus vermiculatus. Other char- . 
acteristic shrubs are Fendlera rupicola Engelm. & Gray, Peraphyllum 
ramosissimum Nutt., Kunzia tridentata, Cercocarpus parvifolius, 
Amelanchier alnifolia Nutt., and Yucca baccata Torr. The alkaline 
flats are covered with chenopodiaceous plants.??_ The foothills up 
to 7500 feet are covered with pinyon pines and cedars. Above 
these come Rocky Mountain yellow pine, forming a distinct zone 
up to gooo feet. 
As in southwestern Colorado, the greater portion of middle and 
northwestern Colorado, up to an altitude of 7500 feet, is covered 
with sage brush, Chrysothamnus spp., and Sarcobatus vermiculatus. 
There is very little grassland country until an altitude of 7000 feet is 
reached. Oak chaparral grows to some extent below 7500 feet, 
but in many localities forms a distinct zone between the pinyon- 
cedar and montane zones. Pinyon pine and cedars are common 
associates here as in other parts of Colorado. On the lower slopes 
cedar is predominant, forming nearly go per cent. of the tree growth; 
at higher altitudes pinyon becomes relatively more abundant. Sage 
brush reaches the height of its development, both in size and numbers, 
on level expanses below 7500 feet; it extends up to 10,000 feet, 
however, being confined to dry ridges. Populus angustifolia, Alnus 
fenutfolia Nutt., Lepargyraea argentea, and Crataegus spp. are com- 
mon streamside plants up to an altitude of 7000 feet. Cercocarpus 
parvijolius, Amelanchier oreophila A. Nels., Symphoricarpos spp., 
and Kunzia tridentata occur on-dry and stony hillsides. 
It is generally held that the vegetation and flora of the eastern slope 
is very different from that of the western slope. This is especially 
true for altitudes below 8000 feet. The vegetation of the alpine, 
Subalpine, and to a less extent of the montane zones, however, is 
very similar on both slopes. Below 8000 feet the climatic and zonal 
22 For excellent discussions of the flora and vegetation of the southwestern part 
of Colorado see the following articles: BRANDEGEE, T. S., The flora of southwestern 
Colorado. Bull. U.S. Geol. and Geog. Surv. of the Territories (Hayden Survey) 11: 
227-248. EAstwoop, Atice, Report on a collection of plants from San Juan County 
in “nec Utah. Proc. Cal. Acad. Sci. 6:270-329. 1896. BAKER, Cart F., 
AND Earte, F. S., Narrative accounts of collecting trips in southern and western 
Colorado in ioe Bakerianae 
