SANTA CLARA VALLEY I SESPE FIELDS. 
61 
maroon measures (Vaqueros); the siliceous shale (Modelo), and the 
Modelo sandstone. The wells penetrate the lower third of the series, 
starting at horizons in or near the top of the lower purple shale and 
reaching perhaps the lower part of the rusty, calcareous sandstone 
which constitutes the upper division of the Sespe formation. It 
may be even that the upper part of the red beds is reached, red 
sand having been encountered in the bottom of some of the holes. 
Fig. 8 indicates the general disposition of these wells. Their pro¬ 
duction has been comparatively large, 200 barrels a day being the 
record of several at the start. Within a year, however, most of 
them decreased to about 60 barrels, and at the present time few 
yield more than 20 to 30 barrels a day and many much less. The 
gravity of the oil is about 32° B.—the same as that of the Tar Creek 
wells. 
The feature of especial interest in regard to the Fourfork wells is 
their altitude, coupled with the fact that they derive their oil from 
the same general zone, although from a somewhat different horizon, 
as the Tar Creek wells to the east and those of the Foot-of-the-Hill 
district to the west. This indicates an undulation of the oil table 
or the altitude at which the oil stands in the same bed. 
TAR CREEK WELLS. 
The Tar Creek wells are located in the southwestern portion of the 
Tar Creek amphitheater, which is drained by several tributaries flowing 
directly into this stream, including one of its principal branches 
known as Bear Creek. The wells number between 20 and 30, but 
are now mostly abandoned, their yield having fallen to but 3 or 4 
barrels a day. Originally 100 to 200 barrels was the production. 
Like the wells of the Fourfork region, these also are distributed along 
the curve of the strata as they bend about the axis of the Topatopa 
anticline. The local strike varies, however, slightly on either side 
of N. 10° E., and the dip is generally between 25° and 30° SE. The 
strata penetrated are apparently somewhat higher than those of the 
Fourfork region, and these are, therefore, the highest wells thus far 
considered in the Sespe region. One at least starts near the top of 
the gray shale about midway of the Vaqueros formation; the others 
start somewhat lower; a few wells, the shallowest of the group, start at 
a comparatively short distance above the rusty beds of the upper 
division of the Sespe formation. Oil appears to be obtained at depths 
between 230 and 1,700 feet below the surface, in the lower portion 
of the Vaqueros formation or the rusty beds in the upper portion of 
the Sespe. There is evidence, however, that many oil-bearing horizons 
were passed in the younger beds overlying these members. The 
presence of oil in these younger beds is undoubtedly due to the occur¬ 
rence of fine sands or other porous materials, which are distributed 
