62 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
through the series and which form the reservoirs for the collection of 
oil from the more shaly members. The logs of some of the wells 
indicate that a considerable amount of sand had been penetrated by 
the drill, but it is probable that the strata are sandy shale of fine 
grain rather than distinct sandstone. Occasionally red sand has 
been reported from some of the wells at depths less than 1,000 feet, 
but it is probable that this is the purple or reddish shale constituting 
the lower part of the Vaqueros formation. 
In the field it was thought that a slight local undulation of the 
beds could be detected in their broad sweep about the axis of the 
general Topatopa anticline. A like occurrence was suspected in 
the Fourfork district. Slight as these are, they should not be disre¬ 
garded in an attempt to collect facts bearing on the conditions under 
which the oil of the Coast Range is found. 
The yield of these wells is very irregular and the accumulation of 
oil is readily pumped off. It is reported by the man in charge of the 
wells that they are affected by rain, the yield increasing materially 
after a heavy fall. 
POLE CANYON. 
LOCATION. 
Pole Canyon, although but 2 miles from Sespe Creek, lies wholly be¬ 
yond the area of disturbed rocks that are so well developed at the 
entrance to the gorge of the Sespe. Although no productive wells 
have yet been drilled in this territory it is deemed advisable to include 
here a short discussion of its structure, as it connects two productive 
areas and may at some future time be found on careful prospecting to 
be itself an oil-producing region. 
GEOLOGY AND STRUCTURE. 
PI. II , sec. F-F', is illustrative of the conditions along the lines 
F-F' of the general map (PI. I) which are practically those prevailing 
along Pole Canyon. At the north end of the section, on the eastern 
flank of Hopper Mountain, the southern and western edge of an 
extensive outcrop of Modelo sandstone is seen. South of this outcrop 
is a narrow belt of Vaqueros shale which is locally crumpled into an 
asymmetric anticline. South of the Vaqueros area the Modelo forma¬ 
tion reappears, turned past the vertical at the crest of the ridge east 
of Pole Canyon, but quickly regaining its southerly dip in the slopes 
below. At the lower edge of the outcrop there is some confusion in 
the succession of strata and in the dips and it is believed that a slight 
displacement has taken place in addition to an overthrow. The over¬ 
throw is best observed in the upper Modelo sandstone, which out¬ 
crops in a continuous half circle, the axis of the fold pitching about 
45° SE. In this sandstone also is well shown the principal syncline of 
