2 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA, 
students of the physical geography of North America, they must be here 
indicated with some detail, since an understanding of the nature of the 
Gravel deposits of the Sierra depends so much on an acquaintance with the 
physical peculiarities of the region over which they are distributed. 
Let us assume as the central point of our picture of the topography of 
California its most striking feature, “The Great Valley,’ and from this let 
us then extend our view first to the region immediately adjacent to it, — its 
edge, so to speak,—and then to the more remote portions of the State, which 
indeed have but little geographical or geological connection with it, or with 
the subject of the present volume. 
The Great Valley —the valley of the Sacramento and San Joaquin rivers 
— forms an area of almost level land, having a roughly elliptical form, trend- 
ing about N. 30° W. and §. 30° E., and embracing about 18,000 square miles. 
It lies between latitudes 34° 50’ near Fort Tejon, and 40° 40’ near Shasta, 
having an extreme length of 450 miles and an average width of forty. The 
shape of the area of flat land, between the foot-hills of the mountains which 
enclose it, is somewhat irregular. The base of the Sierra Nevada on its east 
side has a pretty regular trend north of latitude 35° 30°; but south of this it 
bends around towards the west, and thus, meeting the Coast Range, closes 
up the southern end of the valley. The northern end is also closed by the 
convergence of the Sierra and Coast Ranges, the latter chain assuming a 
northerly trend from Clear Lake north, while that of the Sierra continues 
the same beyond the limits of the valley. Above Red Bluff, indeed, the 
ranges approach each other very nearly, the volcanic overflow from the 
Sierra coming quite down to the Sacramento at this point; while a little 
farther north this river almost touches the foot-hills on the eastern side of 
the valley, and is only a few miles distant from them on the west. A section 
across the valley, in the direction of its length, shows that the fall of the 
Sacramento River, from Redding to its mouth, a distance of 192 miles, is 
556 feet; while that of the southern portion of the valley, between Kern 
Lake and the mouth of the San Joaquin, a distance of 260 miles, is 282 feet. 
The fall of the Sacramento River, within the limits of the Great Valley, is 
therefore about three times as rapid as that of the river system which drains 
the southern section. Indeed, the lower or most southeastern portion of 
the Great Valley, usually called the Tulare Valley, is very nearly a level 
plain, occupied in part by shallow lakes. Of these Tulare Lake is the largest, 
having an area of 687 square miles and a depth of only about forty feet. 
