Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

GEOLOGY.
the borings are carried, increases from the base of the hills towards the bay, and many of the
wells are bored down through the salt water of the bay.
None of these Artesian borings have been carried downwards into the sandstone strata; they
only pierce the superficial drift or alluvium. Several veins or strata of water are generally
found; and when the borings first commenced, an overflow was generally obtained.
The formations that are successively passed in boring, are sands and clays, and the water is
found to rise from the sandy strata alone. Towards the Mission, a very heavy and thick formation of blue clay is met with, containing roots and leaves partly decomposed, and giving off a
disagreeable odor. This clay is over fifty feet thick, and water is found below.it. The configuration of the underlying strata of sandstone and shale is highly favorable to the success of
Artesian borings in the overlying drift or detrital accumulations. It is possible that water
could also be obtained from the slaty layers between the compact sandstone strata; but the
drilling of the rock would be attended with great expense, and it is questionable whether the
formation is not so compact and dense as to prevent rapid infiltration, or a subterranean flow of
water.
Some of the wells in the city are eighteen inches in diameter, and cased with cast-iron pipes;
others have a simple and temporary lining of sheet-iron like a stove-pipe. The cost of the
wells, complete, with the ordinary lining, is about four dollars per foot. 1
At the villages of Santa Clara and San Jose, Artesian borings have been entirely successful.
At San Jose, during the past winter, (1853,) the earth was bored to a depth of seventy-eight
feet, through the fine alluvial clay of that valley. At that depth, the auger suddenly dropped
into a stratum of water and sand, and, on being withdrawn, the water followed it to the surface and overflowed freely. The column has since been raised several feet by the addition of
pipes, and an elevation sufficient to irrigate the surrounding lands is attained. No diminution in the volume of water discharged has yet been observed; but several other wells are about
being sunk, which will perhaps reduce the quantity.
Several other wells have been constructed with satisfactory results. One of the borings was
remarkably successful; at the depth of about seventy-five feet, a rush of water to the surface
took place, and has continued to overflow without diminution. Such is the pressure and force
with which this water rises, that it has been found difficult to control it and prevent it from
overflowing the adjoining grounds. Another is reported to have been sunk to the depth of two
hundred and twenty-five feet, and to yield seventy-five gallons a minute. The drainage from
the different wells forms a brook large enough to drive a saw-mill. The success attending the
Artesian borings in that alluvial valley is so general, and the advantages obtained are so great,
that they are becoming very numerous. The Artesian wells can also be constructed at an
expense that of ordinary wells.
1 I am indebted for many of these facts to Mr. Hopkins, who has been engaged in boring wells in San Francisco for two
years past. (February, 1854.)
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