74 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
It is therefore possible that in the Santa Maria district the gas pres¬ 
sure is the chief agent in giving the oil mobility, and that the condition 
of the rocks is the chief factor that controls the matter of where the oil 
is stored most abundantly. Hydrostatic pressure may not play an 
important part. The especially large accumulations in anticlines 
may be accounted for primarily by the cavities offered b}^ the strata 
along upward folds, and secondarily by the presence of less pervious 
beds arching over such folds and affording favorable conditions for the 
confinement of oil and gas tending to escape. Lesser stores of oil may 
occur at other points within the formation. 
INDICATIONS OF OIL. 
The chief criteria for judging as to the presence or absence of oil in 
appreciable quantities in this region have-been the attitude of the beds, 
their position in the series, and the surface indications. Other minor 
evidences of- a local nature have also been taken into account. In 
drawing conclusions from structural indications anticlines have been 
considered as the chief factors favoring accumulation, inasmuch as the 
oil appears to have gathered in them in a majority of the proved occur¬ 
rences in this district, other conditions being favorable. The conclu¬ 
sion has been reached that anticlines afford a fairly trustworthy clew 
to the location of the most important oil deposits. Close folding 
appears to play a part in this district in depriving the rocks of their 
oil, and excessive disturbance and fracturing is unfavorable to its 
retention. But, on the other hand, moderate folding would appear 
to be favorable, if not requisite, for the accumulation of stores of oil, 
and probably the most favorable conditions are afforded by anticlinal 
folds of such sharpness as to render the brittle rocks porous by frac¬ 
turing, but to leave less pervious arches of more elastic rock. 
The second criterion is the statigraphic position in the formation of 
the beds exposed over the area in which oil is sought. As has been 
before stated, the oil-bearing strata occur chiefly in the lower portion 
of the Monterey. Where the outcropping beds belong to the higher 
portion of the formation there is a greater likelihood that the under¬ 
lying oil-bearing strata have been able to retain their contents than 
where the lower strata have been denuded of the greater part of the 
overlying beds or where they are themselves exposed or partially 
removed. 
As regards the third criterion, the chief surface indications are 
afforded by the presence of seepages of oil or tarry material from the 
shales, by asphalt deposits, bituminous shales, and burnt shale. 
Asphalt occurs mainly in three ways—as a mixture of bituminous 
material with sand, due to the absorption by overlying sand deposits 
of seepages from the shale, as hardened fillings of asphalt in cavities 
along joints, and as excessively saturated shale. The burnt shale is 
