SANTA CLARA VALLEY: TAPO FIELD. 89 
No evidence of the red and gray banded series of probable Eocene 
age lias been found in any of the holes in this field. 
TAPO WELLS. 
Wells have been drilled in the main fork of Tapo Canyon and also 
in each branch of a westerly tributary. Those at present producing 
lie along the east fork of this tributary. They are four in number, 
although from their designation, Nos. 12 to 15 inclusive, it is to be 
inferred that several others have been in existence in earlier days. 
Indeed, one or two of these old wells still contain a slight amount of 
oil. The producing wells are sunk in northward-dipping sandstone 
and shale a mile north of the axis of the Tapo anticline. They yield 
at present from 5 to 40 barrels of oil per day. The gravity is 20° to 
24° B., the 20° oil being produced by the well highest up in the canyon 
and lowest as to the strata penetrated. These wells are about 200 
feet apart and range in depth from 460 to 1,200 feet. The oil sand is 
encountered at 235, 465, 940, and 865 feet, from the well farthest up 
the creek to that lowest down, respectively. The wells lowest on the 
dip are the greatest producers. The dip of the measures is from 50° 
to 60°, and it is impossible to say that a single bed produces oil for the 
entire field, although this is suggested by the increasing depths of the 
wells in the direction of the dip. More or less water is pumped with 
the oil, and it is the opinion of the superintendent that the two are 
mined and come from the same bed. The amount of water, how¬ 
ever, is slight, the proportion being given as 1 of water to 40 of oil. 
Inasmuch as water-bearing sands overlie the oil sands it may be that 
a leak occurs which would account for its presence with the oil. 
Water was also found beneath the oil sand in the well farthest up the 
gulch and has been encountered in some of the wells now abandoned. 
All the wells yield gas, the deeper the well the greater the quantity. 
The whole of the lower half of the Vaqueros strata exposed in Tapo 
Canyon shows a greater or less impregnation with petroleum. No 
unusual amount appears to have been assembled in proximity to the 
axis of the main anticline, and it may be that the productive territory 
is a particularly rich portion of the series of beds which, from some 
cause or other, has held its oil better than the great mass of the beds 
in the region. From the surface no reason can be seen for the enrich¬ 
ment of one portion of the formation over another portion, and except 
for strong seepages in proximity to the wells one locality might as 
readily have been chosen for development as another. 
The logs of the Tapo wells show a succession oi blue clay, brown 
shale, gray sandstone, fine to coarse, and in one instance a trace of 
conglomerate. The thicknesses of these several materials, which are 
constantly repeated, vary from 5 to 200 or more feet, the average 
being, perhaps, between 20 and 75 feet. 
