Phytogeographical notes on the Rocky Mountain region 
|, Alpine region 
P, A. RYDBERG 
The alpine region, roughly speaking, is the region between the 
perpetual snow and the timber line. 
THE UPPER LIMIT, THE PERPETUAL SNOW LINE 
A perpetual snow line cannot be spoken of in the southern 
Rockies. Even the highest peaks do not have a perpetual snow 
cap like Mt. Shasta or Mt. Hood. This is probably due to the 
less amount of moisture and precipitation. It is true that many 
of the peaks have perpetual snow on them, but this snow is mostly 
in the form of snow-drifts and small glaciers, especially on the 
northern or northeastern side. The amount of snow depends to a 
great extent on local conditions, as for instance on an exposure > 
to the northwestern winds or partial protection from the direct 
action of the summer sun. The Snowy Range of Colorado has 
more snow than the much higher Gray’s Peak, Sierra Blanca, or 
Mount Massive. In the Canadian Rockies and especially in the 
Selkirk Mountains the conditions are different and more like those 
of the European Alps. There the highest peaks have a perpetual 
snowcap and the glaciers extend far down in the valleys. In 
northern Montana, as for instance in the Sperry Glacier region, are 
found the only places in the United States where in the Rockies 
there are glaciers of any great extent, notwithstanding the fact 
that the Montana mountains are considerably lower than those of 
Colorado. ; 
THE LOWER LIMIT, THE TIMBER LINE 
The timber line is by no means a well-defined boundary line. 
It is in reality a broad zone in which the woody vegetation gradually 
thins out from the dense forest to the last krumholz. In 
nature there is not found any sharp line between two regions, but 
only a gradual transition zone between them. 
