3 G 
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, Khett, 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 tliis 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, 
