STRUCTURE AND CONDITIONS AFFECTING PRESENCE OF OIL. 77 
rather uniformly along the northeastern border of the area, and de¬ 
velop toward the southeast into the syncline crossing Tunnel Canyon 
and Horse Gulch just north of Sisquoc River. The high, broad ridge 
between Bone Mountain and Manzanita Mountain is composed of 
Monterey shale, which lies approximately flat, and toward the north¬ 
west becomes one arm of the great syncline which extends through 
Goodchild’s ranch on Labrea Creek and is traceable almost to Colson 
Fork of Tepusquet Creek. A similar syncline, possibly the same, 
extends from Colson Fork northwestward across Tepusquet Creek to 
the margin of the Lompoc quadrangle. The northeastern arm of this 
fold forms the high ridge extending along the southwestern side of 
Buckhorn Canyon. 
It is possible that the pre-Monterey rocks north of Bee Rock Can¬ 
yon plunge down monoclinally under the Yaqueros in a fold at right 
angles to the wide anticlinal fold that exposes the former. Such a 
plunge would be apt to give rise to the northeast-southwest table 
between Bone Mountain and Manzanita Mountain that interrupts the 
structure to the northwest and southeast, and this table may, there¬ 
fore, represent a buckling across an otherwise continuous structure. 
Southwest of Los Coches Mountain one or more folds are over¬ 
turned, but the northwestern extensions of these folds have not been 
examined. 
The region southeast of Round Corral and Asphaltum creeks is 
occupied by several sharp folds which strike in a general northwest- 
southeast direction. Overturning is not uncommon in this series of 
folds, one notable example being an anticline on the southern flank 
of Zaca Peak. West of Round Corral Creek the structure lines bow 
around from a northwesterly to a westerly or west-southwesterly 
direction, the folds at the same time becoming less compressed and 
the conditions for the retention of the oil in the basal sands of the 
hard shale series correspondingly better. 
FAULTS. 
There is strong evidence of a fault zone passing north of the nar¬ 
row area of intrusive rock north of Zaca Lake, and thence north¬ 
westward as far as the head of Rattlesnake Canyon. The resultant 
downthrow along this zone of displacement is on the southwest, 
probably amounting to a good many hundred feet toward the east 
edge of the Lompoc quadrangle. Toward the northwest this fault 
apparently dies out or merges into a sync line. 
Just east of Los Coches Mountain there may be another fault 
which brings* up the uppermost Vaqueros on the north. A third 
fault between the Pliocene and Monterey may extend from a point 
near the mouth of Round Corral Canyon to Labrea Creek. 
1784—Bull. 322—07-6 
