570 
GENERAL NOTES ON THE CLIMATE. 
The climate of the district between the Rocky mountains and the Cascade range, comprising 
much the largest portion of Oregon and Washington Territories, has many of the characteristics 
peculiar to mountain regions. These seem to belong to the low plain and valley of the Columbia 
much more than to the Missouri valley and plains at Fort Benton, and their distinguishing points 
of great daily range of temperature and abrupt changes of wind and weather are as conspicu¬ 
ous in the journal of the expedition along the eastern base of the Cascade mountains as in the 
record at St. Mary’s valley. This line of reconnaissance was but little elevated above the sea 
at most points. 
The Cascade range has a most decisive effect on the climate of the district east of it, which is 
mainly due to its great elevation and high latitude. The equable temperatures of the immediate 
coast would otherwise be felt as far inland as in the corresponding European districts, where 
they directly control the climate of nearly half the continent. The Pacific coast has this local 
feature abruptly changed by the intervention of these mountains, and the modification of climate 
which remains is only felt in the generally high temperature of the western portion of the conti¬ 
nent. All portions of the western border of the continent, even from the Mississippi river, parti¬ 
cipate in these higher temperatures at all altitudes, and the great elevation of the mountain ranges 
and plateaux there has alone obscured this fact. It does not, however, render the contrasts 
peculiar to arid valleys and the vicinity of high mountains less conspicuous, though the mean of 
their temperatures is much higher. 
Thus, the mean temperatures at St. Mary’s and in the dry plain of the Columbia are greater 
than those of the coast, if the lowest scale of allowance for altitude be applied; yet the range of 
successive months is very great, and the range of simple extremes even greater than these last 
in proportion. 
The high summer temperatures of this region are scarcely less noticeable than on the plains of 
the Missouri, though the daily range is so much greater here as to distinguish the climates as 
quite unlike. All the plain of the Columbia, though but little elevated above the sea, appears to 
participate in the abrupt daily changes peculiar to mountain regions, and this is doubtless mainly 
due to the great altitudes of the Cascade and Coast mountains, which shut it from the coast of 
the Pacific. 
The several detailed reports in connexion with special reconnaissances show that the climate 
of the mountain districts is generally milder than would elsewhere belong to corresponding lati¬ 
tudes and altitudes. Mountainous districts on the eastern portion of the continent in these lati¬ 
tudes would present records of temperatures much lower and more severe. It is, however, not 
less extreme in its changes, and generally not less profuse in precipitation for the prominent 
ranges. Those near the coast arrest a very large precipitation at all seasons, and are sufficiently 
elevated to convert most of it into snow, except in the three months of summer. As the inter¬ 
vening plains, before reaching the Rocky mountains, are so low, there is comparatively little of 
rain or snow on them, and the higher portions of the Rocky mountains must again receive a 
large precipitation. East of the mountains the quantity of rain or snow in the extreme seasons 
of summer and winter is but a very small amount, and the profusion is mainly in spring and 
early summer. 
These records show greater correspondence of the districts east of the Cascade range of 
mountains with those of the mountain plateaux southward, in regard to local aridity and to the 
attendant daily extremes of temperature, than could have been anticipated of so high a latitude. 
These peculiarities do not seem dependent on altitude alone, also, as they belong as decidedly lo 
the low plain of the Columbia as to the Great Basin at 4,500 feet elevation above the sea. 
At the coast of the Pacific the daily and monthly ranges of temperatures are very small, and 
the climate at Puget sound has the equable features without the unpleasant peculiarities of that 
of the California coast. The humidity and amount of precipitation is very great in comparison 
with the interior, and greater when measured by the per-centage of humidity, and the number of 
