GEOLOGICAL SURVEY OF THE TERRITORIES. 331 



ton it reappears essentially the same in structure as farther south, and 

 is here traversed by the Willamette and Cowlitz Rivers. 



These two sections of this great valley have now free drainage to the 

 Pacific, through the Golden Gate and the trough of the Columbia, both 

 of which are channels cut by the drainage water through mountain bar- 

 riers that formerly obstructed 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 char- 

 acter to the surface of our Western Territory, and that have now almost 

 all been drained away and disappeared. 



East of the California Valley the Sierra Nevada lies, like a lofty 

 mountain chain, reaching all the way from our northern to our southern 

 boundary. The crest of the Sierra Nevada is so high and continuous 

 that for one thousand miles it shows no passes less than five thousand 

 feet above the sea, and yet at three points there are gateways opened 

 in this wall, by which it may be passed but little above the sea level. 

 These are the canons 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 cut- 

 ting down of this barrier has progressed to such an extent as almost 

 completely 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 ter- 

 tiary and even cretaceous ages. This we learn from the fact that strata 

 belonging to these formations cover its base, but reach only a few hun- 

 dred 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 reposi- 

 tories of the gold that has made California so famous among the mining 

 districts of the world. 



East of the Sierra Nevada we find a high and broad plateau, five hun- 

 dred miles in width, and from four thousand to eight thousand feet in 

 altitude, which stretches eastward to the base of the Rocky Mountains, 

 and reaches southward far into Mexico. Of this interior elevated area 

 the Sierra Nevada forms the western margin, on which it rises like a 

 wall. It is evident that this mountain belt once formed the Pacific 

 coast ; and it would seem that then this lofty wall was raised upon the 

 edge of the continent to defend it from the action of the ocean waves. 

 In tracing the sinuous outline of the Sierra Nevada, it will be seen that 

 its crest is crowned by a series of lofty volcanic cones, and that one of 

 these is placed at each conspicuous angle in its line of bearing, so that it 

 has the appearance of a gigantic fortification, of which each salient and 

 reentering angle is defended by a massive and lofty tower. 



The central portion of the high table-lands to which I have referred 

 was called by Fremont the " Great Basin," from the fact that it is a 

 hydrographic basin, its waters having no outlet to the ocean. The 

 northern part of this area is drained by the Columbia; the southern by 

 the Colorado. Of these the Columbia makes its way into the ocean by 

 the gorge it has cut in the Cascade Mountains, through which it flows 

 nearly at the sea level ; while the Colorado flows to the Gulf of Cali- 

 fornia through a series of canons, of which the most important is nearly 

 one thousand miles in length, and from three thousand to six thousand 

 feet in depth. In volume 6 of the Pacific Railroad Reports I have 



