CHAPTER IV. 



GEOLOGY OF PIT RIVER AND KLAMATH BASINS. 



PlT RIVER BASINS. LAKE-LIKE CHARACTER OF THE LOWER BASIN. PROOFS THAT IT HAS ONCE BEES A LAKE. INFUSORIAL SEDIMENTS 



DEPOSITED BY ITS WATERS. RANGE FORMING THE UPPER CANON OF PIT IlIVER. SECOND BASIN OF PIT RIVER. INFUSORIAL MARLS. 



HlLLS OF METAMORPHIC SLATE, GREENSTONE, PORPHYRY, AND TRAP BORDERING FIT RIVER. GEOLOGY OF THE COUNTRY ABOUT THE 



HEAD OF PITBIVEB HOT SPRINGS AND INFUSORIAL MARLS. KLAMATH BASINS TYPICAL ILLUSTRATIONS OF THE GEOLOGICAL STRUCTURE 



OF A GREAT AREA. COMMON FEATURES OF THE REGION LYING EAST OF THE SIERRA NEVADA AND CASCADES. XOT ONE BUT MANY 



BASINS. KLAMATH BASINS ONCE LAKES. LOCAL GEOLOGY. PIT RIVER TO WRIGHT LAKE. RECENT VOLCANIC CONE. CLIFFS RORDER- 



ING RHETT LAKE OF SANDSTONE AND TRAP. EFFLORESCENCE ON THE SHORES OF RHETT LAKE. THE NATURAL BRIDGE A FAULT. 



INFUSORIAL MARLS OF LOST RIVER AND LOWER KLAMATH LAKE. METAMORPHIC FORM OF THESE MARLS RESEMBLING JASPER. GEOLOGY 



OF THE SHORES OF KLAMATH LAKE. BASALTIC CONGLOMERATE ON KLAMATH RIVER. INFUSORIAL MARLS. PUMICE. TRAP RANGE3 



SOUTH AND EAST OF KLAMATH MARSU. PUMICE PLAIN BETWEEN KLAMATH MARSH AND THE DBS CHUTES RIVER. 



LOWER BASIN OF PIT EIVER. 



FROM the summit of the conical mountain, which I have mentioned as overlooking the 

 entrance to the lower canon of Pit river, we for the first time looked down into one of the 

 series of areas which give character to the immense region which has been denominated the 

 Great Basin. This conical mountain formed a portion of a subordinate axis of the range we 

 had crossed, and of which Lassen s butte forms the most elevated point. This range constitutes 

 the western wall of the first of the basins of Pit river, and runs off with a northwesterly trend 

 in the direction of Mount Shasta, which was plainly visible from the point where we stood. 



In the east rose from this plain another wall, similar to that which I have described, and 

 having nearly the same trend. Toward the south, these two ranges coalesced, and were lost in 

 the peaks composing the Sierra Nevada. On the north low ranges of mountains bounded the 

 horizon, but the exact limits of this plain, in that direction, could not be determined. Its 

 surface seemed as level as water, and, but that it was covered with grass, it had every appear 

 ance of a large lake, enclosed on every side by bold and rocky shores. The only exit from this 

 wide area, as proved by its drainage, is through the deep chasm which Pit river has formed in 

 its western wall. 



It required no stretch of the imagination to see that, at a comparatively recent period, this 

 basin had been what it now so much resembled, a lake, whose waters had gradually been with 

 drawn through the deepening channel of its present draining stream. As we descended to the 

 plain, our conjectures of its history were confirmed by its geological structure. Its surface, 

 which is nearly level, is everywhere underlaid by a series of fine infusorial marls, similar to 

 that which occurs in the canon of Pit river. These marls are apparently horizontally stratified, 

 and as the channels of the streams which cross the plain have cut them to a depth of but a few 

 feet, it was impossible to determine their thickness. Exposed at various points, they exhibited 

 great uniformity of color and texture, being pure white or light brown, and all of them con 

 taining, in large quantities, the remains of fresh water Diatomacece. In the examination of the 

 structure of this basin, many points of analogy with that of the Sacramento valley suggested 

 themselves. It has the same elongated form, is bounded by similar parallel mountain ranges, 

 having nearly the same trend. It is drained by streams which unite in the same way to force a 



