PHYSIOGRAPHY AND LIFE ZONES. 23 



squirrel occupies the lower part of the zone, as do also to some extent 

 the mantled ground-squirrels and yellow-bellied and big-tailed chip- 

 munks. 



The conspicuous birds are the ptarmigan, rosy finches, pipits, sis- 

 kins, crossbills, and white-crowned sparrows, while many of the 

 Canadian Zone species come into the lower edge of the zone, and 

 golden eagles are often seen around the peaks and dill's. 



ARCTIC-ALPINE ZONE. 



The Arctic-Alpine Zone caps the peaks and extends on cold slopes 

 below many of the passes to 7,000 feet and on warmer slopes to 8,000 

 feet. It lies entirely above the last trace of timber and dwarfed 

 trees and includes most of the glaciers and large snow fields, great 

 expanses of barren cliff and rock, and also extensive areas of thin soil 

 and depauperate vegetation. P'or the greater part of each year it 

 is buried in snow, but during the short summer every available bit 

 of fertile soil is carpeted with green or is bright with alpine flowers, 

 and even the cracks and niches in the rocks shelter hardy plants that 

 defy wind and storm and fi'osty nights. 



There are no trees or upright shrubs, but many of the plants have 

 woody stems and most have unusual root development to enable them 

 to withstand such adverse climatic conditions. Several species of 

 dwarf willow's grow as carpets wnth leaves and stems flat on the 

 ground and each plant sends up a single tiny catkin of flowers and 

 fruit, often less than an inch from the surface of the ground. Cush- 

 ions of mountain pinks {Silene acaulis) lend color to the slopes 

 as do also the deep blue Jacob's-ladder, and dwarf blue columbine, 

 the alpine harebell, the little fragrant beds of forget-me-nots, many 

 species of saxifrage, a delicate pink spring beauty, a dwarf bitterroot, 

 tiny crimson shooting stars, yellow Sibhaldia, buttercups, and cinque- 

 foils. 



Of mammals there are none restricted to this zone, though in 

 summer the white goats and mountain sheep spend their days mostly 

 in it, usually coming down into the edge of the Hudsonian to feed at 

 night, and in winter the goats remain chiefly on its wind-swept 

 ridges. Hoary marmots and alpine chipmunks often run up into it 

 but really belong to the zone belo^y. 



Birds of many species fly over and wander into the. zone, but the 

 only one breeding entirely within its boundaries is the gray-crowned 

 rosy finch. The ptarmigan and pipit are often found high in this 

 zone in summer, but apparently breed mainly lower down in the 

 Hudsonian. 



