OIL OF THE SANTA MAE IA DISTRICT. 
109 
by the oil-yielding Monterey. The surface evidence of such a condi¬ 
tion is most conclusive. What effect local flexures either in the Mon¬ 
terey below the Pismo or in the Pismo itself will have on the produc¬ 
tion, only drilling will determine. According to Fairbanks’s interpre¬ 
tation of the structure of the area, the depth at which the oil will be 
struck ought to decrease from the middle of the area toward both 
the northeast and southwest. The only well fully tested in the region 
yields 500 barrels of 14° oil per day, so that the prospects for the de¬ 
velopment of a good field are unusually bright. 
As the Monterey shale underlying the Pismo of the Arroyo Grande 
field is continuous with the Monterey mapped in the Lompoc quad¬ 
rangle northeast of the Santa Maria Valley, it is reasonable to suppose 
that there are considerable portions of this great belt of Monterey 
that will prove productive. The local structure is usually the deter¬ 
mining factor in the accumulation of the petroleum, so that a thor¬ 
ough knowledge of this is essential to economical test drilling. 
HUASNA FIELD. 
The Huasna field lies east of the Arroyo Grande field and north of 
the Lompoc quadrangle. Prospect drilling is now going on in this 
region, but with what results the writers are not able to say. During 
a very hasty trip through this region in the summer of 1905 the senior 
writer noted great areas of Monterey shale, with some interbedded 
coarse granitic sandstones, in many places of considerable thick¬ 
ness. Such conditions are ideal for the accumulation of petroleum 
if the beds are not too sharply folded. This Monterey area is prob¬ 
ably the continuation of that exposed in the northeastern part of the 
Lompoc quadrangle, and may connect the latter with the Monterey 
area east of Arroyo Grande and also with that covering the summit 
of the Santa Lucia Range a few miles east of San Luis Obispo. It is 
to be regretted that no maps adequate for showing the structure of 
the formations in the region east of the San Luis quadrangle and 
north of the Lompoc quadrangle are available. Without these it 
will be impossible to do for this region such detailed geologic and 
structural mapping as has already been done for the two quadrangles 
mentioned. 
OIL, OF THE SANTA MARIA DISTRICT. 
ORIGIN. 
There is no doubt that the petroleum in the Santa Maria dis¬ 
trict is indigenous to the Monterey shale. Bitumen is a character¬ 
istic part of that formation throughout its wide extent over an area 
covering hundreds of square miles, and there is no other formation 
1784—Bull. 322—07-8 
