SANTA CLARA VALLEY: HOPPER-PIRU FIELDS. 
67 
The fold next north of the Modelo anticline is the syncline that 
passes south of Pirn Peak. It may be seen both on the west side of 
the divide and east of the peak in the upper portions of Blanchard 
Canyon. The crumpling is slight and the dip on either side of the 
axis comparatively gentle. 
North of this syncline is another anticline of importance, the axis 
of which passes east and west across Lime Canyon. The heart of this 
fold is occupied by the lower Modelo sandstone, which is here exposed 
over an area of 3 or 4 square miles. It is surrounded by the overlying 
shale, which in the divide north from Piru Peak forms scarcely more 
than a thin film. To the east across Piru Creek the shale is succeeded 
by the upper Modelo sandstone, and this in turn by the still higher 
siliceous shale at the top of the Modelo; finally the heavy mass of the 
Fernando sediments sets in, arching about and over the eastward- 
pitching axis of the fold. 
The northernmost fold along this section within the Camulos quad¬ 
rangle, with the exception of one or two minor crumples, is the Rea- 
soner syncline, the axis of which occupies Reasoner Canyon. This 
flexure disappears, however, in the divide at the head of the creek, 
where the heavy lower Modelo sandstone lies in a broad arch about the 
axis of the Top atop a anticline. To the east the syncline continues for 
an undetermined distance beyond Piru Creek, being conspicuous in 
the Fernando conglomerate and sandstone in the hills between Santa 
Felicia and Devil canyons. Both slopes of the syncline are gentle, 
the dip generally being less than 40°; but there are areas in which this 
is somewhat increased by local crumpling. 
The northernmost of the folds described in the preceding para¬ 
graphs and others beyond the confines of the Camulos quadrangle all 
fade into or are developed as minor crumples on the general easterly 
slope of the main Topatopa anticline. 
Within the region here described the three prominent anticlines, the 
Hopper, the Modelo, and the Lyons, have proved oil bearing, the 
Modelo being the most productive, perhaps on account of its greatest 
development; the Lyons less so, and the Hopper the least. On the 
Hopper fold, however, there is at the present time but a single well of 
low yield. 
STRUCTURE EAST OP PIRU CREEK. 
The region east of Piru Creek presents a number of approximately 
east-west folds, some of which, particularly the more northerly, are 
continuations of those lying west of the stream already described, 
while others farther south are apparently restricted almost wholly to 
the area east of Piru Creek, only their extreme points extending west¬ 
ward across the stream. Of the latter, the Holser anticline is the most 
conspicuous. The axis of this fold lies in the hills a little south of 
