644 THE ANCIENT LAKES OF WESTERN AMERICA: 
drainage to the Pacifie, through the Golden Gate and the 
trough of the Columbia, both of which are channels cut by 
the drainage water through mountain barriers that formerly 
obstrueted its flow, and produced an accumulation behind 
them that made these valleys inland lakes; the first of the 
series I am to describe of extensive fresh-water basins that 
formerly gave character to the surface of our Western Terri- 
tory, and that have now almost all been drained away and 
have disappeared. ; 
East of the California Valley lies the Sierra Nevada; a 
lofty mountain chain reaching all the way from our north- 
ern to our southern boundary. The crest of the Sierra Ne- 
vada is so high and continuous that for a thousand miles 
it shows no passes less than five thousand feet above the sea; 
and yet, at three points there are gate-ways opened in this 
wall, by which it may be passed but little above the sea-level. 
These are the eaüons of the Sacramento (Pit River), the 
Klamath and the Columbia. All these are gorges cut 
through this great dam by the drainage of the interior of the 
continent. In the lapse of ages the cutting down of this 
barrier has progressed to such an extent as almost com- 
pletely to empty the great water basins that once existed 
behind it, and leave the interior the arid waste that it is— 
_ the only real desert on the North American Continent. 
The Sierra Nevada is older than the Coast Mountains, 
and projected above the ocean, though not to its present 
altitude, previous to the Tertiary and even Cretaceous ages. 
This we learn from the fact, that strata belonging to these 
formations cover its base, but reach only a few hundred feet 
up its flanks. The mass of the Sierra Nevada is composed 
of granitic rocks, associated with which are metamorphic 
slates, proved by the California Survey to be of Triassic and 
Jurassic age. These slates are traversed in many localities 
by veins of quartz, which are the repositories of the gold 
that has made California so famous among the mining dis- 
tricts of the world. 
