GEOLOGY OF SW. IDAHO AND SE. OREGON. 
[BULL. 217. 
CLIMATE AND VEGETATION. 
The leading characteristics of the climate of the portions of Idaho 
and Oregon here considered are : Small precipitation ; generally cloud- 
less skies; hot, dry summers; and moderately cold winters, during 
which there is some rain and snow, but not enough to make the mean 
annual precipitation large. Something of the nature of the prevailing 
climatic conditions may be judged from the following data, compiled 
from the report of the United States Weather Bureau for 1900, which 
pertain to localities within or near the region here discussed. 
Locality. 
Weather records for the //car 1900. 
Boise, Idaho 
Garnet, Idaho. __ 
Payette, Idaho . . 
Baker City, Oreg 
Burns, Oreg 
Silver Lake, Oreg 
Vale, Oreg 
Precipi- 
tation. 
Inches. 
12.77 
s. 11 
10.60 
|:',.s| 
6.57 
9.21 
Temperature. 
Mini- Maxi- 
mum, mum. 
Mi'iin. 
Deg. F. Deg. /•'. Deg. /•'. 
11 104 52 
14 
10 
-1 
1 

8 
ii>! 
53. 7 
95 47.3 
99 46. 1 
98 I 46.4 
Kil 49.4 
Killing frost 
Last in 
spring. 
First in 
aiitumn. 
Apr. 28 Oct. 23 
Apr. 26 Oct. 2. r 
Apr. 13 Sept. 21 
May 29 
Sept. 26 
May 16 
Aug. 8 
(«) 
(«) 
May 26 
Sept. 18 
Snow. 
Tnehes. 
20.1 
19.8 
12.8 
15.5 
"Temperature helow '.\;1 V. every month. 
All the localities mentioned in the above table are situated in val- 
leys. On the mountains cooler and more humid atmospheric condi- 
tions prevail. The snowfall is light in the valleys and, like the mean 
annual precipitation, increases with elevation, but not in a direct and 
simple ratio. The general climatic conditions of both Idaho and 
Oregon vary in a conspicuous manner at different localities. In Idaho 
the northern and more mountainous portion of the State is much colder 
and more humid than the intensely arid southern portion. In Oregon 
aridity is the prevailing condition in the southeastern and central 
parts of the State, with increasing humidity toward the west and 
northeast. The portion of each State here described, while character- 
istic of its most arid valleys and most desolate mountains, must not 
be considered as representative of the entire political division of 
which it forms a part. 
The most conspicuous effect of increase in elevation on climatic 
conditions in the region discussed is an increase in precipitation, 
particularly in snowfall. While in spring and early summer the 
snow lingers on the mountains long after it has disappeared from 
