THE STRUCTURE OF THE VALLEYS OF SACRAMENTO AND SAN JOAQUIN.
These valleys form a “single geographical formation,� stretching from the terminal spurs of the Cascade Mountains at the north to the junction of the Sierra Nevada with the southern terminus of the Monte Diablo range with the thirty-fourth parallel of north latitude. The length of the valley is about three hundred and eighty miles in length on an air line, with a breadth of fifty miles at its widest point.
The general appearance of the valley is that of an extended plain composed of alluvium, and this opinion would obtain in the mind of any person whose line of travel would lead him over the lower terraces of the plain, or what is denominated its bottom lands. It is only by making a transverse section of this plain that we should be able to arrive at any correct conclusions of its structure and peculiarities of its formation; by pursuing this course, very distinctive and marked features are observable of different periods of elevation to which this portion of the country has been subjected subsequent to its emergence above the level of the sea.
The character of the soil in many parts of this valley will render it of little importance as an agricultural district, unless water in ample quantities for irrigation can be obtained. (These remarks apply particularly to the upper terrace of the valley on each side of the river.) And we hope that attention may be called to this very important subject of making the extensive areas of the arid districts of the basin available for market and agricultural purposes.
Experience has demonstrated the almost certainty of obtaining water, and in sufficient quantities, for agricultural and other purposes, in all valleys resting upon sedimentary formations, and having a basin-shaped structure, and where the different beds have a degree of uniformity or regularity in their position, and are of a texture that will admit the free percolation of water through the superior beds, and sufficiently firm to prevent its escape in those below.
These conditions are all fulfilled in the basin of the Sacramento, and from the united testimony of different observers, we have ample evidence that the sedimentary formations of one side are the same as those upon the other, with the exception, perhaps, of the conglomerate.
The report, after classifying the rocks of the coast, mountains, &c., goes on to describe their order and more recent volcanic rocks. In relation to the discovery of coal, the author says:—
From a careful examination of this part of the country, with this object in view, I feel no hesitation in saying that coal will not be found in any part of the coast mountains south of the thirty-fifth parallel of north latitude; what there may be north of this point, I know nothing, having never visited it.
It is not unfrequent, in passing over the country, to hear of beds of mineral coal; during the past season I have visited four such localities, and, as was anticipated, each of them proved to be merely small beds of lignite, and two of them hardly deserving that name. One of these deposits proved to be but a bed of leaves, having a thickness of about three inches, resting upon a tertiary sandstone containing marine shells, and covered with twelve feet of a sandy alluvium. This is one of those coal beds which has figured so largely in the public prints of the State during the past year, and has induced several gentlemen to pay the locality a visit, and to return as deeply disappointed as their previous anticipations were elevated.
The report of coal veins in the Coast Mountains must be received with many grains of allowance, and, at the best, none but tertiary deposits will be found, and these, even should they exist, would be capable of supplying but a limited demand, and that usually of an inferior quality.[34]