GEOLOGY — KLAMATH BASINS. 



37 



and coverd, to a considerable depth, surfaces which are now exposed. The streams which flowed 

 from these areas had greater volume, and flowed from a higher level than at present. To this 

 cause we may attribute the deep channels which they have cut' through the resistant material of 

 the mountain barriers which opposed their progress to the ocean. 



In all their general features, the basins of the Klamath lakes closely copy those of upper 

 Pit river. They form elongated troughs, lying between nearly parallel mountain ranges, of 

 which that on the west is broken through by Klamath river, which reaches the ocean through 

 a cation as deeply cut as that of Pit river. The bottom of this trough is covered — to how great 

 a deplh we do not know — by a series of stratified deposits, altogether similar to those which 

 I have described. The drainage of this basin^has, however, been less complete than that of 

 the Sacramento and upper Pit river, and large portions of its surface are still occupied by 

 bodies of water. 



LOCAL GEOLOGY. 



The geology of the interval between Pit river, at the point where we left it, and Wright lake, 

 is exceedingly monotonous. Four or five miles north of Pit river we lost all traces of the older 

 volcanic rocks, to which I have referred as occurring in that vicinity ; and from that point 

 northward, for thirty miles we passed over a succession of plateaus of vesicular trap, precisely 

 like that which occurs so abundantly about Fort Beading, this being apparently the form 

 which the volcanic material always assumes when poured out in floods of considerable depth on 

 to surfaces not covered by water. 



Near Wright lake occurs a conical mountain of trap rock, which rises to a height of perhaps 

 1,500 feet from the plain on which it stands. The south shore of this lake is bordered by a 

 mountain range of nearly equal altitude, which has here a course nearly east and west; 

 curving round towards the north, its western extremity terminates in a bold headland on the 

 shore of Rhett lake, and is connected by a low ridge, with similar hills, lying north of these 

 lakes. This connecting ridge, forming the barrier between Rhett and Wright lakes, is com- 

 posed exclusively of trap, and bears on it a conical hill of blood-red scoria, which has 

 evidently at no distant day formed^a volcanic vent. 



Rhett lake is bordered on the east and north by cliffs of considerable height, of which the 

 base is composed of light-colored sandstone, theupper portion of trap. This sandstone, which 

 is very soft and friahle, belongs to the series of infusorial marls of which I have so frequently 

 spoken. 



On the eastern shore of the lake is a conical hill, considerably removed from the cliffs referred 

 to, but having apparently the same structure. It is composed at base of sandstone, regularly 



niLL OF SANDSTONE, CAITED WITH TRAr, EODETT UKE. 



stratified, and nearly horizontal, and is capped with trap. Both the trap and sandstone were 

 doubtless once connected with the similar strata in the cliffs, now nearly half a mile removed. 

 We have here evidence of an amount of erosion which can hardly be attributed to the action of 



