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22 Muhlenbergia, Volume 3 
The temperature records of minus 2 and minus 4.5 degrees 
would appear to be exceedingly cold for late summer months, 
as we usually have some of our warmest weather in the valley 
at that season. Certain it is that the night temperatures are 
exceedingly variable. While encamped for botanical purposes 
on the mountain top for two weeks in the latter part of August 
and the first week of September of 1905 at an elevation of 
10000 feet, we were greatly surprised to find that during some 
nights a thin blanket was more than was necessary to keep us 
comfortable, while the succeeding night we piled on four heavy 
blankets, and even then were somewhat uncomfortable. So far 
as could be observed, the atmosphere was the same, cloudless 
and still. Enough has been said to give one an idea of the con- 
ditions under which the plants on this mountain survive. 
GEOLOGY 
The mountains surrounding the valley are for the most part 
composed of rocks of igneous origin, with occasional outcrop- 
pings of metamorphic rocks interspersed among them. ‘These 
consist largely of rhyolite, andesite and granite. The reddish- 
brown coloring of the mountains on the north and east sides of 
the valley indicate a preponderance of rhyolite, while the dark 
gray of the eastern Sierra presents the appearance of andesite 
and granite formations to a greater extent. At the extreme 
southern end of the valley, at Steamboat Springs, where hot 
spring action has been and is still prevalent, there is a mixture 
of all of the above, making this point especially interesting from 
the standpoint of plant growth. 
The floor of the valley consisting as it does of huge boul- 
ders and sedimentary rocks, gives evidence of former river action 
and the presence of an ancient lake. ‘The outcroppings of diat- 
omaceous rock along several cuts in the railroad would help to 
substantiate this theory. 
I am indebted to Mr: W. S. T. Smith, Professor of Geol- 
ogy, University of Nevada, for verifying the above statements. 
Ee 
——— Os 
