50 



NORTH AMERICAN FAUNA. 



[NO. 16. 



from the zone below, so that the usual zone relations are chan<ie(l, 

 I)arallel strips of Canadian and lludson'an ruuninji' up and down the 

 mountain — instead of encircling it in the usual liorizontal belts. Along 

 Squaw Creek another tongue of alpine heialock descends to the head 

 of the main fall, at an altitude of about 1,2~A\ feet, and is siniihirly 

 sandwiched between ascending tongues of Shasta lirs. 



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 'Bed Butte.' It is about li,()0(> feet below the altitude of 

 extreme timberline and its summit is covered witli 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 i)lants as O.tyrla d'ujyna and Saxifnuja tolmin. In this case the 



-K^-^ii; 



S^. 



Fig. 29. — Dwiii'l iiiiir.-, fiidiiiL; al)rui)tl.v Jlloug cold east side i<t' ri(lj;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 alford perhaps the simi)lest exami)le 

 of the direct influence of slope exi)osure. The warm west sides of these 

 ridges usually bear trees in i)r<)])ortion to the availability of their slopes, 

 while the cold cast sides remain naked and alpine (see lig. 14). The way 

 the (hvaif pines stop along the east crest of the ridges is shown in the 

 acconi[)anying figure (fig. "29). 



Fiiuilly, the glaciers of Shasta afford impressive evidence of the 

 effects of slope exposure. .My party did not take the altitudes of fhe 

 ghutiers, but accoi'ding to the Shasta map sheet of the U. S. Geological 

 Survey those on the <'old east and norfheast slopes descend below 

 9,000 feel, and one of them, at the liead oi" Ash Creek, below s,r,{n) feet, 

 while the only one having a south exposure^ (at the head of Mnd 

 Creek) stops at 11,000 feet,' and theic ar<' no glaciers at all on the west 



'There is another i^liuiei- on tlic south side, tributary to Mnd Creek, which 

 descends lower than the one marked on the niaj) as * Konwakitoii f^liicicr/ bnt it 

 is fomitli'tely hid(hni l>y a hij^li riduo and is not e\])o8ed to the kite afternoon sun. 



