50 NORTH AMERICAN FAUNA. [No. 16. 
from the zone below, so that the usual zone relations are changed, 
parallel strips of Canadian and Hudsonian running up and down the 
mountain—instead of encircling it in the usual horizontal belts. Along 
Squaw Creek another tongue of alpine hemlock descends to the head 
of the main fall, at an altitude of about 7,250 feet, and is similarly 
sandwiched between ascending tongues of Shasta firs. 
Between ‘The [South] Gate’ and the grove of alpine hemlocks on 
upper Squaw Creek is a prominent mass of lava 700 or 800 feet high, 
known as ‘Red Butte.’ It is about 2,000 feet below the altitude of 
extreme timberline and its summit is covered with trees; nevertheless 
its precipitous northeast side is so cold that its zone position is well 
above timberline, as shown by the presence there of such distinctively 
alpine plants as Oxyria digyna and Saxifraga tolmiet. In this case the 
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ead iaiie BP te es we 
(eo WE s rie a ——— —_|| 
Fic, 29.—Dwart pines ending abruptly along cold east side of ridge. 
F 
effect of a very cold mass of rock is added to that of the coldest slope, 
and the result is a lowering of alpine zone species 2,000 feet below their 
normal elevation on the hottest southwest slopes. 
The high north and south ridges afford perhaps the simplest example 
of the direct influence of slope exposure. The warm west sides of these 
ridges usually bear trees in proportion to the availability of their slopes, 
while the cold east sides remain naked and alpine (see tig. 14). The way 
the dwarf pines stop along the east crest of the ridges is shown in the 
accompanying figure (fig. 29). 
Finally, the glaciers of Shasta afford impressive evidence of the 
effects of slope exposure. My party did not take the altitudes of the 
glaciers, but according to the Shasta map sheet of the U. 8. Geological 
Survey those on the cold east and northeast slopes descend below 
9,000 feet, and one of them, at the head of Ash Creek, below 8,500 feet, 
while the only one having a south exposure (at the head of Mud 
Creek) stops at 11,000 feet,' and there are no glaciers at all on the west 
1There is another glacier on the south side, tributary to Mud Creek, which 
descends lower than the oue marked on the map as ‘Konwakiton glacier,’ but it 
is completely hidden by a high ridge and is not exposed to the late afternoon sun. 
