36 GEOLOGY PIT RIVER VALLEY — KLAMATH BASINS. 



we crossed immediately after leaving Pit river, on our route to Klamath lakes, are composed of 

 a blue, hard, highly metamorphosed silicious slate. A few miles further north occurs a 

 beautiful variety of porphyry, of which the ground work is chocolate color, the crystals of 

 felspar, white, and of large size. In a greenstone dyke, near the same locality, I found small 

 quantities of green carbonate of copper. The plutonic rocks exposed on Pit river, where we 

 left it, are apparently older than the floods of lava-like trap which have covered so much of the 

 country traversed before reaching that point. Here, rather than anywhere else on the line of our 

 route to the Columbia, I should expect to find veins of quartz and talcose slates, which are so 

 frequently the repositories of gold. From the rolled fragments brought down by Pit river, as 

 well as from specimens brought in by our hunters, who followed the river to a higher point than 

 where we left it, it is evident that there exists in this vicinity a protrusion of granite, and 

 associated with it, the porphyries, quartz, greenstone, &c, of which I have spoken. 



Beyond this range of hills Pit river traverses, and rises in, a region which, over a large area, 

 exhibits precisely the same features as that through which we have followed it. 



Lieutenant Williamson, while connected with an exploring party which visited this vicinity 

 some years since, followed up Pit river to its source, and traversed the plain in which Goose 

 lake is situated, from his detailed and clear description of the country I learn that the white, 

 chalk-like marls, which form so marked a feature of the geology of the lower plains of Pit river, 

 recur at various points near its source above, as below, in lake-like plains, which are separated 

 by walls of volcanic rock. The plain about Goose lake is of the same general character with 

 those we have passed over. Pit river takes its rise in a series of hot spring, which, in their 

 character and surroundings, apparently resemble those of the Des Chutes Basin, to which I 

 shall soon have occasion to refer. 



From a gentleman whom I had the pleasure of meeting at Fort Beading, and who had 

 recently passed over the country lying between Fort Hall and Goose lake, I obtained valuable 

 information, and specimens illustrative of the geology of his route. From these it is evident 

 that the geological structure of the region bordering lower Pit river affords a complete illustra- 

 tion of that of a large portion of country lying east of it. 



KLAMATH BASINS. 



Like the plains of Pit river the several areas, in which are set Wright, Rhett, and the 

 Klamath lakes, exhibit the typical features of the structure of the entire region with which they 

 are inseparably connected, and which, with very imperfect notions of its character, has been 

 denominated the Great Basin. This immense area, cut in various directions by ranges of low 

 mountains and hills, has, by this and other causes, been divided into many subordinate districts, 

 each of which, possessing some characters peculiar to itself, has, also, many features which are 

 common to all. They all form portions of the same great plateau to which allusion has already 

 been made, and which exhibits everywhere a remarkable unity of geological structure, of 

 climate, and in its flora and fauna. 



Of the many secondary basins which go to make up this area, those which lie nearest the 

 base of the mountain wall, on the west, receive a larger share of the rain precipitated upon it 

 than those which are more remote. As a consequence, the supply of water received through 

 the year is greater than the annual evaporation, and this excess flows off in the streams which 

 lead from them. At a period not very remote in the history of our continent, the amount of 

 water falling into the Klamath and Pit river basins was, probably, much greater than now, 



