CHAPTER XVII. 
GEOLOGICAL OBSERVATIONS ON OREGON AND 
NORTHERN CALIFORNIA. 
Tue student of physical geography who obtains his ideas of moun- 
tains from maps, often imagines that the elevated chain is a narrow 
line of lofty heights, with a distinct foot, steep declivities and pointed 
summits. The chain of Western America, as commonly delineated 
on charts, appears to be confined to a strip of land not over fifty miles 
wide; and mountains in other parts of the world are generally made 
to occupy nearly the same limits, whatever their extent. ‘The slopes 
are all reduced to a map-maker’s standard. 
The errors flowing naturally from this source are nowhere greater 
than in the case of the Rocky Mountains; and the correction of any 
false impression thus derived is of the first importance, as introduc- 
tory to a study of Oregon. The range is placed in our charts from six 
to eight hundred miles from the coast, and it seems to stand like a 
crested wall raised to a vast height between the east and west, with 
rapid slopes of thirty, forty, or fifty degrees. 
The traveller crossing these ridges, finds, on the contrary, as many 
of them have informed us, that he commences his ascent soon after 
leaving the valley of the Mississippi; and as he travels onward, 
although meeting with ridges and valleys as well as.extensive plains, 
still he makes an increasing rise; and when the position marked for 
the Rocky Mountains is reached, he has already ascended seven or 
eight thousand feet, though hardly conscious of it during his progress. 
There are now high ridges in most parts to be crossed, unless he follow 
some of the passes ; yet these ridges are seldom over four or five thou- 
sand feet in altitude. Beyond them a descent commences like that on 
the east; and although broken by high, rugged mountains in some 
places, it is still a gradual descent, which is hardly finished before 
