CHAPTER II. 



GEOLOGY OF THE SACRAMENTO VALLEY. 



General features. — Structure of the coast mountains. — Trap, serpentine, and granite. — Auriferous slates. — Structure 



OF SIERRA NEVADA. OLDER THAN COAST MOUNTAINS. — MeTAMORFIIIC LIMESTONE. AURIFEROUS ROCKS. PLACER DEPOSITS.— 



Alluvial plain. — Localgeology. — Vacaville to ciiico cf.eek — Gravelly plains. — Alluvial soil and terraces of putos 



and cache creeks. banks of the sacramento. b.ed color of tuba river w ant of stone at marysville — sacramento 



euttes. — cliico creek. — fossillfl.eol's sandstone. interesting mingling of fossils. — strata probably cretaceous. 



Trap hills. — Streams absorbed by the plain. — Volcanic phenomena. — Lava streams. — Crater. —Obsidian. — Fort read- 

 ing. — Trap hills. — Tufaceous conglomerate. — Cretaceous rocks near shasta city. — Ammonites batesii. — Carboniferous 

 limestone. fossils. 



GENERAL FEATURES. 



The area which has received this name constitutes the north half of what might properly he 

 called the great Californian valley, forming a continuous trough, lying hetwcen the converging 

 axes of the two great ranges of Californian mountains, and of which the northern and southern 

 halves would he inseparable were it not that, draining to the centre, they are respectively 

 traversed hy the rivers Sacramento and San Joaquin ; and hence, for convenience, have been 

 distinguished from each other hy the names of these streams. This great valley, which has a 

 length of 350 miles, and a maximum breadth of 50 miles, may be regarded as affording in its 

 structure and origin a typical example of the manner in which — formed by common causes — all 

 the principal valleys of the far west have been produced. All may be said to occupy the elon- 

 gated areas enclosed between the separated but inosculating ranges of mountains, having nearly 

 the same common trend. 



Of these valleys the Gulf of California is the most southern and the largest. Though its floor 

 is now below the ocean level, and its mountain boundaries do not quite enclose it, it presents a 

 marked similarity of general structure to the others to which I have alluded — the valleys of 

 San Francisco and Sacramento — and, to carry the comparison still further, to the second double 

 valley, that of the Cowlitz and Willamette. 



The mountain chains which enclose the Sacramento valley are the coast mountains on the 

 west, and the Sierra Nevada on the east. Between these it lies as a broad plain, of which the 

 central portion is scarcely raised above the level of the sea, while the remote ends are scarcely 

 more than twice as many feet above as they are miles distant from the centre. The greater 

 part of the fall of the draining streams being confined to the vicinity of the ends of the valley, 

 as a consequence, through most of the length, the current of these streams is slow, their course 

 tortuous, and their borders, especially near their point of exit, are marshy and covered with 

 wide expanses of tulc, (bullrush.) 



Surface and soil. — The centre of the valley is occupied by a broad alluvial plain, with little 

 diversity of level, of which the soil is generally fine and fertile, but sometimes coarse, gravelly, 

 or stony, and barren. The more fertile surface is covered with a growth of wild oat, or grasses, 



