16 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
do not offer adequate explanation. For these drill holes, figure 1, D, 
which shows a water-filled sand lens with free outlet at the lower end 
but sealed at the upper, is suggestive. Under these conditions a 
negative head or partial vacuum would be created, and if such a 
sand were penetrated by the drill the drilling water might be taken 
up as fast as it could be poured into the well. These conditions do 
not depend on the complete sealing of the upper end of the lens, for 
the same principle w^ould operate to a lesser degree providing only 
that the outlet is larger and accommodates more water than the 
intake. As the freedom of circulation normally decreases with 
depth, the outlet might have to be considerably greater than the 
intake, but this relation is probably no less common than the reverse, 
by which a high positive head would be developed. 
It may be mentioned in passing that many geologists believe that 
meteoric and connate waters are confined to a relatively shallow zone 
near the earth’s surface, below which the rocks are normally dry. 
The literature of ore deposits contains many references to this belief 1 
and strong evidence in favor of it is also found in the Appalachian 
oil fields. In the fields of San Joaquin Valley, however, large amounts 
of water have been found at the greatest depths reached, more than 
4,000 feet, in the fields of the west side, and 5,000 feet in the Kern 
River field. 
- v / 
RELATION TO THE OIL. 
The lenticular rocks overlying the oil in the San Joaquin Valley 
fields include a number of well-recognized water sands. These sands 
may be traced within small areas, though wide correlations are impos¬ 
sible. Numerous factors influence the distribution of the water and 
the course of its circulation and therefore where irregular and len¬ 
ticular rocks are concerned it is impossible to predict in advance of 
drilling where the greatest flows will be found. 
The ground-water level, or the plane below wdiich most of the strata 
are saturated, varies from place to place but is generally within 300 
feet of the surface. Between this level and the horizon of the oil 
from one to a dozen or more water sands are found, the number 
depending on the locality and on the depth of the oil. In some local¬ 
ities no flows are encountered in the 300 feet or more of strata directly 
above the oil, but in others there is a water sand less than 50 feet 
above it. Sands yielding large quantities of water are generally 
encountered below the oil, the distance depending somewhat on the 
thickness and character of the oil zone itself. Where the oil is con¬ 
fined to sands in one zone 300 feet or more thick, there is generally a 
water sand between 10 and 100 feet below the base of the oil zone. 
1 One of the earliest papers is that of Kemp, J. F., The r61e of the igneous rocks in the formation of 
veins: Am. Inst. Min. Eng. Trans., vol. 31, pp. 1G9-198, 1902. 
