CHAPTER IV. 
GEOLOGY OF FIT GIVER AND KLAMATH BASINS. 
Pit river basins.—Lake-bike character op the lower basin.—Proofs that it has once been a lake.-—Infusorial sediments 
DEPOSITED BY ITS WATERS.—RANGE FORMING THE UPPER CANON OF PIT RIVER.—SECOND BASIN OF PIT RIVER.-INFUSORIAL MARLS.— 
Hills of metamorphic slate, greenstone, porphyry, and trap bordering pit river.—Geology of the country about the 
HEAD OF PIT RIVER.-IIoT 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.—NOT 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 RANGES 
SOUTH AND EAST OF KLAMATH MARSH.-PUMICE PLAIN BETWEEN KLAMATH MARSH AND THE DES CHUTES RIVER. 
LOWER BASIN OF PIT RIVER. 
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 hounded the 
horizon, hut the exact limits of this plain, in that direction, could not ho determined. Its 
surface seemed as level as water, and, hut that it was covered with grass, it had every appear¬ 
ance of a large lake, enclosed on every side by hold 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 hut a few 
teet, 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 Dlatomacece. 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 
