CHAPTER II. 
GEOLOGY OF THE SACRAMENTO YALLEY. 
General features.—Structure of the coast mountains.—Trap, serpentine, and granite.—Auriferous slates.—Structure 
OF SIERRA NEVADA.-OLDER THAN COAST MOUNTAINS.-METAMORrHIC LIMESTONE.—AURIFEROUS ROCKS.-PLACER DEPOSITS.- 
Alluvial plain.—Local geology.—Vacaville to chico cf.eek.—Gravelly plains.—Alluvial soil and terraces of putos 
and cache cref.ks.—Banks of the Sacramento.—Bed color of yuba river —Want of stone at Marysville.—Sacramento 
buttes..—Ciiico creek.—Fossilifi.kous 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 between 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 by the rivers Sacramento and San Joaquin ; and hence, for convenience, have been 
distinguished from each other by 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 hut 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 tide , (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, hut sometimes coarse, gravelly, 
or stony, and barren. The more fertile surface is covered with a growth of wild oat, or grasses, 
