GEOLOGY. 
65 
and believes to antedate the Knoxville. It is closely associated and 
intermingled with bodies of diabase and gabbro. This complex 
forms Point Sal Ridge and the rocky headland of Point Sal. Another 
complex that he believes belongs in the Knoxville forms a long dike 
north of Schumann Canyon. It is an exceedingly complicated intru¬ 
sive mass of gabbro and peridotite that has been penetrated by later 
dikes of diabase, norite, gabbro, and intermediate types of rock. 
The areas mapped as Franciscan (Jurassic) are largely occupied by 
serpentine that was originally intruded in Franciscan strata. This 
serpentine may be older than the Knoxville, and the last-mentioned 
occurrence of gabbro and peridotite may be contemporaneous with it. 
Diabase was struck at a depth of 1,300 feet in the Pezzoni well 
No. 1, southwest of Sisquoc. It is a considerably altered rock com¬ 
posed largely of serpentine and plagioclase feldspar, with some augite, 
possibly a small amount of unaltered olivine, considerable magnetite, 
and several accessory minerals. This occurrence is of considerable 
importance as affecting the prospects for the production of oil in 
this neighborhood. The question arises whether this diabase has 
intruded the Monterey, as in the San Rafael Mountains, or whether 
it is a part of the older igneous formations, in which diabase is 
common. The fact that the rock is so much altered probably indi¬ 
cates that it belongs to a formerly exposed older formation upon 
which a fairly high portion of the Monterey shale series has over¬ 
lapped. It is hardly conceivable that an intrusion at such a depth 
in the shale could have undergone so much alteration. In either 
case, whether this diabase marks the base of the Monterey or whether 
the shales have been intruded by an igneous mass, the conditions are 
unfavorable for the discovery of oil in the immediate vicinity. 
IGNEOUS ROCKS INTRUDING THE MONTEREY. 
The youngest igneous rocks occurring in the Santa Maria quad¬ 
rangle and those of chief interest in the present connection are intru¬ 
sive in the Monterey (middle Miocene). Such are five small areas of 
diabase mapped by Fairbanks south of Point Sal and two areas of 
diabase in the San Rafael Mountains. The age of the two latter is 
somewhat in doubt, but the metamorphic and disturbed appearance 
of the Monterey shale in their vicinity indicates that they originated 
as dikes intruding the Monterey. The shale appears hardened and 
baked in the immediate neighborhood and narrow tongues of Mon¬ 
terey shale, certainly altered along the contact, extend into the mass 
on Tepusquet Creek. Along its edges appear patches of Aucella- 
bearing sandstone belonging to the Knoxville, which were probably 
brought up from below by the intrusion. The diabase in both areas 
is of dark-green color and coarse texture and exhibits sheared ser- 
pentinous facies. 
